BACKGROUND
semelparity  has generally been studied from a demographic perspective that directly contrasts semelparity and iteroparity.
cole  <cit>  found that the fitness advantage gained by an iteroparous over a semelparous strategy was very slight; a semelparous organism had to produce only a single additional offspring to offset the advantage of surviving to reproduce again.
this finding was initially puzzling because it implied that semelparity should be common.
later authors noted that differential juvenile-to-adult mortality, age-specific schedules of reproduction and other life-history traits affect the fitness of the semelparous habit  <cit> .
more recently, iteroparity and semelparity have also been thought to be endpoints of a continuum of life histories  <cit> .
there is mounting empirical support for this continuum hypothesis; semelparous species display significant reproductive variation, and many reproductive modes are not “pure” or “classical” semelparous or iteroparous habits.
some semelparous organisms facultatively reproduce a second time .
for organisms subject to seasonal variation in living conditions, this second bout can occur either:  within the same season as the first  bout, where it has been loosely termed “secondary reproduction” or “partial semelparity”  <cit> ; or  in a subsequent season, where it has been termed “facultative iteroparity”, or “facultative polycarpy” in plants  <cit> .
to avoid confusion between these terms, in this paper we refer exclusively to “secondary reproduction”, operationally defined as a second, non-continuous reproductive episode in an organism considered to be semelparous.
this is meant to encompass both within-season “secondary reproduction” and true “facultative iteroparity”.
we also refer to an occurrence of secondary reproduction or facultative iteroparity as a “secondary reproductive episode” or sre.
here, we investigate the life-history significance of sres in lobelia inflata.
that a semelparous organism may be facultatively capable of reproducing more than once is surprising because the general benefit of semelparity is theorized to be the gain of a demographic advantage through a simultaneous, exhaustive reproductive episode  <cit> .
identifying the conditions under which secondary reproduction or facultative iteroparity may occur is correspondingly important.
the most common explanation for sres is that they are an adaptively plastic response to environmental stressors that constrain primary reproduction.
under conditions where normal semelparous reproduction may result in lost reproductive effort, deferral of reproductive effort to a second reproductive bout can realize fitness gains  <cit> .
we term this the “adaptive deferral hypothesis”.
according to this explanation, since the sre is elicited as an adaptively plastic response to constrained reproduction, semelparous organisms capable of sres should display ‘pure’ semelparity only under ideal  conditions; constraints on primary reproduction should result in deferral of reproductive effort to a second bout.
an important corollary to this explanation is that the likelihood that reproductive effort will be deferred to a sre  is proportional to the severity of the restriction of primary reproduction.
therefore, according to the adaptive deferral hypothesis, sres should:  be expressed at more opportune times than primary reproductive episodes, since deferral of reproductive effort to an equally or more greatly constrained time would not increase fitness; and  show a proportional relationship between the degree to which reproductive effort is deferred to an sre and the degree of constraint on the primary reproductive episode.
several studies have supported the ability of the adaptive deferral explanation to account for sre display.
for example, when primary reproduction was artificially restricted in the crab spider lysiteles coronatus, mothers compensated by reducing reproductive effort invested in the primary reproductive episode, and deferred reproductive effort to a second  <cit> .
there is also evidence for a positive relationship between the degree of reproductive constraint and the expression of secondary reproduction - in a study of the semelparous eresid spider stegodyphus lineatus, schneider et al.
also artificially restricted primary reproduction  <cit> , but did so at different times – either at two or ten days after hatching.
in these studies, both of which were performed in the lab, the authors found that the likelihood of observing a sre was proportional to the severity of restriction of primary reproduction.
in the field, the latent capacity to facultatively express an sre has been observed in the erpobdellid leeches erpobdella octoculata <cit>  and nephelopsis obscura <cit> .
the most common alternative explanation for secondary reproduction is that semelparous organisms with a recent evolutionary transition from iteroparity to semelparity, or with a highly plastic expression of parity, may display reproduction a second time when the fitness cost of doing so is not high.
we term this alternative explanation the “transitional hypothesis”, since it emphasizes the continuity between iteroparity and semelparity.
according to this view, sres may occur as part of a presumably adaptive  opportunistic reaction norm: if selection for semelparity is not strong, an sre can realize additional fitness.
this hypothesis implies that, for seasonal monocarps, the expected value of an sre should correlate with the likelihood of being able to successfully complete that sre.
as semelparity is considered to be an adaptation to low adult survival  <cit> , where conditions are not conducive to prolonged adult survival  selection for more complete or extreme semelparity will be favoured over life-histories where adults survive to exhibit sres.
for semelparous organisms in seasonal environments, the timing of reproduction is usually critical, and while plants reproducing early may prolong the reproductive bout in time without losing fitness, the importance of semelparity increases as reproduction is initiated later in the season, since these plants will then under stronger selection for rapid, simultaneous and exhaustive reproduction .
the transitional hypothesis therefore predicts:  that sres may occur at any time, including inopportune times; and  that increased sre display will be associated with earlier primary reproduction.
our focus for this study is the semelparous herb lobelia inflata , which, according to several lines of evidence, evolved semelparity comparatively recently.
semelparity is considered a derived trait elsewhere in the genus lobelia: of  <dig> species of lobelia l. sect.
lobelia,  <dig> are iteroparous, with only l. inflata being consistently reported as semelparous.
l. appendiculata has also been variably described as monocarpic  <cit> ; even so, this character is clearly derived from a polycarpic ancestor  <cit> .
furthermore, lobelia cardinalis, the species most closely related to l. inflata, is iteroparous  <cit> , and previous studies have demonstrated the lability of parity in the genus lobelia <cit> .
fitness in semelparous herbs like l. inflata depends on a schedule of reproduction that exhausts energy reserves just as the season ends; selection on reaction norms governing reproductive strategies is strong and reproducing at the right time is critical  <cit> .
for many monocarps, the developmental transition to reproduction is initiated in response to and depends on the plants’ evolved response to seasonal cues  <cit> .
for l. inflata, transition from a prereproductive vegetative phase to a reproductive phase—marked by the formation of a reproductive stalk and termed “bolting”—occurs in response to seasonal changes in day length and light quality  <cit> .
the timing of initiation of reproduction is critical, since plants need to exhaust accumulated resources before the season ends; plant phenology and offspring phenotype are especially sensitive to the timing of initiation of reproduction  <cit> .
due to this sensitivity, an effective experimental method to restrict the ability for plants to complete primary reproduction without damaging plant tissue is to manipulate photoperiod to manipulate the cue for initiation of reproduction.
we note that restricting primary reproduction might also have been accomplished via flower or inflorescence destruction, but plants generally do not provide maternal care to seeds, and many plants exhibit a compensatory growth response to herbivory or flower destruction that would confound the response to the restriction of reproduction itself, an issue that is avoided by using time restriction to constrain primary reproduction  <cit> .
laboratory experimental studies have an advantage over observational  approaches when it is important to attribute response to a particular agent, or when a question demands extending the observed natural phenotypic range of expression  <cit> .
for l. inflata, an observational study in situ cannot be used to assess the extent to which reproductive effort is deferred, because adverse conditions in the field suppress the expression of sres.
we therefore used a lab-based phenotypic manipulation experiment to study the underlying potential  for plants to express an sre, and thus whether, and to what extent, plants exhausted their reproductive potential before then onset of winter.
for this experiment, we subjected replicate groups of plants in a growth chamber to increasingly severe time constraints on primary reproduction by manipulating the photoperiod and light intensity to mimic the natural changing conditions of the site of collection .
an increase in the expression of sres in response to more severe time constraints during the primary reproductive episode would be consistent with the “adaptive deferral hypothesis” comparable to sres elicited by restricted primary reproduction in other taxa  <cit> .
this hypothesis specifically predicts that sre expression should be proportional to restriction severity; i.e.
the less time a plant has to complete reproduction, the more likely it is to display a sre, and the greater investment it will make in the sre.
alternatively, if sres in l. inflata are a vestigial expression of the iteroparous history of the genus lobelia or an adaptation to an ancestral environment, time-restricting primary reproduction should be negatively correlated with sre expression if sres waste reproductive potential , or should be uncorrelated if sres have little or no fitness cost.
it should be noted that, even if results show that sres are not effective as a deferral of reproductive effort, alternative explanations to the vestigial hypothesis exist.
for example we cannot discount the possibility that sres may have been adaptive in ancestral environments , or that sres are adaptive for unknown reasons.
RESULTS
likelihood of sre occurring
according to our binomial logistic regression model, the timing of bolting was a strong predictor of likelihood of sre expression .
the likelihood of sre expression was higher in early-bolting, less time-constrained plants, and lower in late-bolting, more time-constrained plants .
likelihood of sre display did not depend on year or prebolting rosette size .
a second binomial regression—run as a mixed-model analysis with genotype included as an additional random effect—did not explain significantly more variation in the response , and thus genotypic lineage did not predict likelihood of sre expression.
the four bolting groups were experimentally produced using a photoperiod manipulation, and this manipulation was repeated for three years from 2008- <dig>  prebolting plant size was measured as the length  of the longest living leaf of the unbolted rosette.
the regression model significantly predicts likelihood of sre expression .
odds ratios express relative likelihood of sre expression.
*p <  <dig> .
proportion of total fruits allocated to sre
according to a second binomial logistic regression model, the timing of bolting was a strong predictor of the proportion of total fruit expressed during the sre .
this analysis showed that early-bolting, less time-constrained plants expressed a greater proportion of their total fruits in the sre than did late-bolting, more time-constrained plants .
year and prebolting rosette size were not significant predictors of the proportion of total fruits produced during the sre .
this binomial logistic regression analysis was also repeated with genotype included as an additional random effect, but again the resulting mixed model did not explain significantly more variation in the response , and therefore genotypic lineage did not predict the proportion of total fruit expressed in the sre.
the four bolting groups were experimentally produced using a photoperiod manipulation, and this manipulation was repeated for three years from 2008- <dig>  prebolting plant size was measured as the length  of the longest living leaf of the unbolted rosette.
the regression model is a significant predictor of the response .
odds ratios express relative likelihood of fruit being allocated to the sre.
*p <  <dig> .
fruit number
a factorial ancova model including bolting month, prebolting rosette size and year, significantly predicted the mean total number of fruits produced per plant .
tukey hsd tests on bolting group revealed two homogenous subsets; september-bolting plants produced the most fruit , which was significantly more than any other group, with july-bolting plants , august-bolting plants , and june-bolting plants  all producing significantly fewer fruit.
this model indicated that bolting month, year, bolting month*year and prebolting rosette size  were all significant predictors of the response.
timing of sre
sre expression occurred from january to early february the following year.
a large proportion of plants  expressed a sre, all between  <dig> and 127 days after the termination of primary reproduction and apparent senescence .
the overall mean time between the cessation of primary reproduction and the initiation of the sre was  <dig>  days .
because early- and late-bolting plants ended primary reproduction at approximately the same time , sres for all bgs took place at approximately the same time: late january to mid february of the year following primary reproduction.
seed germination
our analysis revealed no phenotypic differences among offspring resulting from primary reproduction and sres with respect to germination fraction  or days to germination .
discussion
the adaptive deferral hypothesis, which predicted that plants under the severest time constraints would be the most likely to express sres, was not supported by our findings.
each of the four measures we assessed in this manipulation study—likelihood of sre expression, proportional reproductive investment in sre, total fruits produced, and timing of reproduction—showed a trend opposite to what would be expected given that the deferral hypothesis were true, and instead were consistent with the transitional hypothesis.
first, we observed that late-bolting, heavily time-constrained plants were less likely than early-bolting, less time-constrained plants to express a sre , and produced proportionately fewer sre fruits if they did .
this pattern is inconsistent with the deferral hypothesis, which predicts that time-restriction of primary reproduction should be positively correlated with both sre expression and investment.
second, although sres were given the opportunity for expression in the lab, they have no opportunity for expression under field conditions in a temperate climate: in our growth-chamber study, reproduction generally ended in october, followed by an inter-reproductive period of over 100 days.
also, plants transplanted from our field site to a glasshouse in october  <dig>  exhibited sres the following january .
it is therefore clear that deferral of reproductive effort to an sre does not contribute to reproductive success, contrary to predictions of the adaptive deferral hypothesis.
in examples where sres are explained by adaptive deferral of reproductive effort, the sre generally takes place either:  shortly after primary reproduction ; or  in the next season, as for the pitcher plant wyeomyia smithii <cit> .
in either case, sres increase fitness because sre occur under conditions that are as or more favourable than the conditions under which primary reproduction took place  <cit> .
although in principle it is possible that the inter-reproductive period for l. inflata would be longer under field conditions than it was in the lab, and an sre could occur the following spring, to the best of our knowledge this has not yet been observed.
for these reasons, we conclude that sre expression in l. inflata cannot be accounted for by the adaptive deferral hypothesis.
our results did support the transitional hypothesis, both because sres were produced at an inopportune time, and because the underlying allocation pattern showed that heavily time-constrained plants were less likely to defer offspring than were less time-constrained plants.
if these underlying trends are also expressed in the field, these trends suggest that:  early-bolting plants that opt to defer reproduction may die with significant unspent reproductive potential, representing a substantial fitness cost; and  late-bolting plants compensate for time-constraints by producing flowers more quickly as the season progresses.
furthermore, the observation that no differences in seed viability were detected between primary and secondary reproductive episodes indicates that sres cannot be discounted as simply pseudo reproduction that incurs no energetic costs; this further suggests that any reproductive effort allocated to sres in the field is wasted.
for these reasons, our main conclusion is that sres do not represent an effective avenue for the adaptive deferral of reproductive effort in l. inflata, which is the primary hypothesis explaining why sres exist in semelparous organisms; that deferral results in wasted reproductive effort may have contributed to the evolution of semelparity in l. inflata.
it is important to recognize the limits on the interpretation of data collected under growth-chamber conditions, but also that we are not making assumptions about how sre would be expressed in the field.
it is because we expect the expression of sre to be suppressed under field conditions that we used phenotypic manipulation to expose the trait of interest across a particular array of laboratory conditions.
here, we use photoperiod, a cue known to be ecologically relevant and that elicits a strong reproductive response in l. inflata <cit>  to reveal an otherwise unobservable expression of sre.
we thus make an assumption common to all phenotypic manipulations: that the expression of a trait  will not respond in an opposite manner to a manipulation  in the lab compared to its potential expression in the field.
we focused on photoperiod cues in l. inflata; other cues, correlated with an unknown factor germane to expectation of realized reproductive effort, may influence the developmental decision to defer resources for a sre.
finally, we note that our study was designed to test the adaptive deferral hypothesis, and rejection of this hypothesis does not conclusively establish that sres are maladaptive or nonadaptive in l. inflata.
further study of sre expression in l. inflata elsewhere in its range would allow us to better assess the fitness consequences for plants expressing sres.
CONCLUSIONS
in conclusion, we found that while l. inflata plants had the ability to produce viable seeds in sre fruits, the pattern in which they did so was inconsistent with the adaptively plastic deferral of reproductive effort seen in animal systems: here, time-constraining primary reproduction resulted in semelparity with reduced secondary reproduction.
this norm of reaction is consistent with the expression of vestigial iteroparity that decreases as time constraints increase.
where seasonality is strong and winter is long , sres likely represent a loss of reproductive effort.
thus, secondary reproductive episodes in l. inflata appear to be a vestige of their iteroparous evolutionary past.

 semelparity has generally been studied from a demographic perspective that directly contrasts semelparity and iteroparity. cole found that the fitness advantage gained by an iteroparous over a semelparous strategy was very slight; a semelparous organism had to produce only a single additional offspring to offset the advantage of surviving to reproduce again. this finding was initially puzzling because it implied that semelparity should be common. later authors noted that differential juvenile-to-adult mortality, age-specific schedules of reproduction and other life-history traits affect the fitness of the semelparous habit. more recently, iteroparity and semelparity have also been thought to be endpoints of a continuum of life histories. there is mounting empirical support for this continuum hypothesis; semelparous species display significant reproductive variation, and many reproductive modes are not “pure” or “classical” semelparous or iteroparous habits. some semelparous organisms facultatively reproduce a second time. for organisms subject to seasonal variation in living conditions, this second bout can occur either: within the same season as the first bout, where it has been loosely termed “secondary reproduction” or “partial semelparity”; or in a subsequent season, where it has been termed “facultative iteroparity”, or “facultative polycarpy” in plants. to avoid confusion between these terms, in this paper we refer exclusively to “secondary reproduction”, operationally defined as a second, non-continuous reproductive episode in an organism considered to be semelparous. this is meant to encompass both within-season “secondary reproduction” and true “facultative iteroparity”. we also refer to an occurrence of secondary reproduction or facultative iteroparity as a “secondary reproductive episode” or sre. here, we investigate the life-history significance of sres in lobelia inflata. that a semelparous organism may be facultatively capable of reproducing more than once is surprising because the general benefit of semelparity is theorized to be the gain of a demographic advantage through a simultaneous, exhaustive reproductive episode. identifying the conditions under which secondary reproduction or facultative iteroparity may occur is correspondingly important. the most common explanation for sres is that they are an adaptively plastic response to environmental stressors that constrain primary reproduction. under conditions where normal semelparous reproduction may result in lost reproductive effort, deferral of reproductive effort to a second reproductive bout can realize fitness gains. we term this the “adaptive deferral hypothesis”. according to this explanation, since the sre is elicited as an adaptively plastic response to constrained reproduction, semelparous organisms capable of sres should display ‘pure’ semelparity only under ideal conditions; constraints on primary reproduction should result in deferral of reproductive effort to a second bout. an important corollary to this explanation is that the likelihood that reproductive effort will be deferred to a sre is proportional to the severity of the restriction of primary reproduction. therefore, according to the adaptive deferral hypothesis, sres should: be expressed at more opportune times than primary reproductive episodes, since deferral of reproductive effort to an equally or more greatly constrained time would not increase fitness; and show a proportional relationship between the degree to which reproductive effort is deferred to an sre and the degree of constraint on the primary reproductive episode. several studies have supported the ability of the adaptive deferral explanation to account for sre display. for example, when primary reproduction was artificially restricted in the crab spider lysiteles coronatus, mothers compensated by reducing reproductive effort invested in the primary reproductive episode, and deferred reproductive effort to a second. there is also evidence for a positive relationship between the degree of reproductive constraint and the expression of secondary reproduction - in a study of the semelparous eresid spider stegodyphus lineatus, schneider et al. also artificially restricted primary reproduction, but did so at different times – either at two or ten days after hatching. in these studies, both of which were performed in the lab, the authors found that the likelihood of observing a sre was proportional to the severity of restriction of primary reproduction. in the field, the latent capacity to facultatively express an sre has been observed in the erpobdellid leeches erpobdella octoculata and nephelopsis obscura. the most common alternative explanation for secondary reproduction is that semelparous organisms with a recent evolutionary transition from iteroparity to semelparity, or with a highly plastic expression of parity, may display reproduction a second time when the fitness cost of doing so is not high. we term this alternative explanation the “transitional hypothesis”, since it emphasizes the continuity between iteroparity and semelparity. according to this view, sres may occur as part of a presumably adaptive opportunistic reaction norm: if selection for semelparity is not strong, an sre can realize additional fitness. this hypothesis implies that, for seasonal monocarps, the expected value of an sre should correlate with the likelihood of being able to successfully complete that sre. as semelparity is considered to be an adaptation to low adult survival, where conditions are not conducive to prolonged adult survival selection for more complete or extreme semelparity will be favoured over life-histories where adults survive to exhibit sres. for semelparous organisms in seasonal environments, the timing of reproduction is usually critical, and while plants reproducing early may prolong the reproductive bout in time without losing fitness, the importance of semelparity increases as reproduction is initiated later in the season, since these plants will then under stronger selection for rapid, simultaneous and exhaustive reproduction. the transitional hypothesis therefore predicts: that sres may occur at any time, including inopportune times; and that increased sre display will be associated with earlier primary reproduction. our focus for this study is the semelparous herb lobelia inflata, which, according to several lines of evidence, evolved semelparity comparatively recently. semelparity is considered a derived trait elsewhere in the genus lobelia: of species of lobelia l. sect. lobelia, are iteroparous, with only l. inflata being consistently reported as semelparous. l. appendiculata has also been variably described as monocarpic; even so, this character is clearly derived from a polycarpic ancestor. furthermore, lobelia cardinalis, the species most closely related to l. inflata, is iteroparous, and previous studies have demonstrated the lability of parity in the genus lobelia. fitness in semelparous herbs like l. inflata depends on a schedule of reproduction that exhausts energy reserves just as the season ends; selection on reaction norms governing reproductive strategies is strong and reproducing at the right time is critical. for many monocarps, the developmental transition to reproduction is initiated in response to and depends on the plants’ evolved response to seasonal cues. for l. inflata, transition from a prereproductive vegetative phase to a reproductive phase—marked by the formation of a reproductive stalk and termed “bolting”—occurs in response to seasonal changes in day length and light quality. the timing of initiation of reproduction is critical, since plants need to exhaust accumulated resources before the season ends; plant phenology and offspring phenotype are especially sensitive to the timing of initiation of reproduction. due to this sensitivity, an effective experimental method to restrict the ability for plants to complete primary reproduction without damaging plant tissue is to manipulate photoperiod to manipulate the cue for initiation of reproduction. we note that restricting primary reproduction might also have been accomplished via flower or inflorescence destruction, but plants generally do not provide maternal care to seeds, and many plants exhibit a compensatory growth response to herbivory or flower destruction that would confound the response to the restriction of reproduction itself, an issue that is avoided by using time restriction to constrain primary reproduction. laboratory experimental studies have an advantage over observational approaches when it is important to attribute response to a particular agent, or when a question demands extending the observed natural phenotypic range of expression. for l. inflata, an observational study in situ cannot be used to assess the extent to which reproductive effort is deferred, because adverse conditions in the field suppress the expression of sres. we therefore used a lab-based phenotypic manipulation experiment to study the underlying potential for plants to express an sre, and thus whether, and to what extent, plants exhausted their reproductive potential before then onset of winter. for this experiment, we subjected replicate groups of plants in a growth chamber to increasingly severe time constraints on primary reproduction by manipulating the photoperiod and light intensity to mimic the natural changing conditions of the site of collection. an increase in the expression of sres in response to more severe time constraints during the primary reproductive episode would be consistent with the “adaptive deferral hypothesis” comparable to sres elicited by restricted primary reproduction in other taxa. this hypothesis specifically predicts that sre expression should be proportional to restriction severity; i.e. the less time a plant has to complete reproduction, the more likely it is to display a sre, and the greater investment it will make in the sre. alternatively, if sres in l. inflata are a vestigial expression of the iteroparous history of the genus lobelia or an adaptation to an ancestral environment, time-restricting primary reproduction should be negatively correlated with sre expression if sres waste reproductive potential, or should be uncorrelated if sres have little or no fitness cost. it should be noted that, even if results show that sres are not effective as a deferral of reproductive effort, alternative explanations to the vestigial hypothesis exist. for example we cannot discount the possibility that sres may have been adaptive in ancestral environments, or that sres are adaptive for unknown reasons.  likelihood of sre occurring according to our binomial logistic regression model, the timing of bolting was a strong predictor of likelihood of sre expression. the likelihood of sre expression was higher in early-bolting, less time-constrained plants, and lower in late-bolting, more time-constrained plants. likelihood of sre display did not depend on year or prebolting rosette size. a second binomial regression—run as a mixed-model analysis with genotype included as an additional random effect—did not explain significantly more variation in the response, and thus genotypic lineage did not predict likelihood of sre expression. the four bolting groups were experimentally produced using a photoperiod manipulation, and this manipulation was repeated for three years from 2008- prebolting plant size was measured as the length of the longest living leaf of the unbolted rosette. the regression model significantly predicts likelihood of sre expression. odds ratios express relative likelihood of sre expression. *p <. proportion of total fruits allocated to sre according to a second binomial logistic regression model, the timing of bolting was a strong predictor of the proportion of total fruit expressed during the sre. this analysis showed that early-bolting, less time-constrained plants expressed a greater proportion of their total fruits in the sre than did late-bolting, more time-constrained plants. year and prebolting rosette size were not significant predictors of the proportion of total fruits produced during the sre. this binomial logistic regression analysis was also repeated with genotype included as an additional random effect, but again the resulting mixed model did not explain significantly more variation in the response, and therefore genotypic lineage did not predict the proportion of total fruit expressed in the sre. the four bolting groups were experimentally produced using a photoperiod manipulation, and this manipulation was repeated for three years from 2008- prebolting plant size was measured as the length of the longest living leaf of the unbolted rosette. the regression model is a significant predictor of the response. odds ratios express relative likelihood of fruit being allocated to the sre. *p <. fruit number a factorial ancova model including bolting month, prebolting rosette size and year, significantly predicted the mean total number of fruits produced per plant. tukey hsd tests on bolting group revealed two homogenous subsets; september-bolting plants produced the most fruit, which was significantly more than any other group, with july-bolting plants, august-bolting plants, and june-bolting plants all producing significantly fewer fruit. this model indicated that bolting month, year, bolting month*year and prebolting rosette size were all significant predictors of the response. timing of sre sre expression occurred from january to early february the following year. a large proportion of plants expressed a sre, all between and 127 days after the termination of primary reproduction and apparent senescence. the overall mean time between the cessation of primary reproduction and the initiation of the sre was  days. because early- and late-bolting plants ended primary reproduction at approximately the same time, sres for all bgs took place at approximately the same time: late january to mid february of the year following primary reproduction. seed germination our analysis revealed no phenotypic differences among offspring resulting from primary reproduction and sres with respect to germination fraction or days to germination. discussion the adaptive deferral hypothesis, which predicted that plants under the severest time constraints would be the most likely to express sres, was not supported by our findings. each of the four measures we assessed in this manipulation study—likelihood of sre expression, proportional reproductive investment in sre, total fruits produced, and timing of reproduction—showed a trend opposite to what would be expected given that the deferral hypothesis were true, and instead were consistent with the transitional hypothesis. first, we observed that late-bolting, heavily time-constrained plants were less likely than early-bolting, less time-constrained plants to express a sre, and produced proportionately fewer sre fruits if they did. this pattern is inconsistent with the deferral hypothesis, which predicts that time-restriction of primary reproduction should be positively correlated with both sre expression and investment. second, although sres were given the opportunity for expression in the lab, they have no opportunity for expression under field conditions in a temperate climate: in our growth-chamber study, reproduction generally ended in october, followed by an inter-reproductive period of over 100 days. also, plants transplanted from our field site to a glasshouse in october exhibited sres the following january. it is therefore clear that deferral of reproductive effort to an sre does not contribute to reproductive success, contrary to predictions of the adaptive deferral hypothesis. in examples where sres are explained by adaptive deferral of reproductive effort, the sre generally takes place either: shortly after primary reproduction; or in the next season, as for the pitcher plant wyeomyia smithii. in either case, sres increase fitness because sre occur under conditions that are as or more favourable than the conditions under which primary reproduction took place. although in principle it is possible that the inter-reproductive period for l. inflata would be longer under field conditions than it was in the lab, and an sre could occur the following spring, to the best of our knowledge this has not yet been observed. for these reasons, we conclude that sre expression in l. inflata cannot be accounted for by the adaptive deferral hypothesis. our results did support the transitional hypothesis, both because sres were produced at an inopportune time, and because the underlying allocation pattern showed that heavily time-constrained plants were less likely to defer offspring than were less time-constrained plants. if these underlying trends are also expressed in the field, these trends suggest that: early-bolting plants that opt to defer reproduction may die with significant unspent reproductive potential, representing a substantial fitness cost; and late-bolting plants compensate for time-constraints by producing flowers more quickly as the season progresses. furthermore, the observation that no differences in seed viability were detected between primary and secondary reproductive episodes indicates that sres cannot be discounted as simply pseudo reproduction that incurs no energetic costs; this further suggests that any reproductive effort allocated to sres in the field is wasted. for these reasons, our main conclusion is that sres do not represent an effective avenue for the adaptive deferral of reproductive effort in l. inflata, which is the primary hypothesis explaining why sres exist in semelparous organisms; that deferral results in wasted reproductive effort may have contributed to the evolution of semelparity in l. inflata. it is important to recognize the limits on the interpretation of data collected under growth-chamber conditions, but also that we are not making assumptions about how sre would be expressed in the field. it is because we expect the expression of sre to be suppressed under field conditions that we used phenotypic manipulation to expose the trait of interest across a particular array of laboratory conditions. here, we use photoperiod, a cue known to be ecologically relevant and that elicits a strong reproductive response in l. inflata to reveal an otherwise unobservable expression of sre. we thus make an assumption common to all phenotypic manipulations: that the expression of a trait will not respond in an opposite manner to a manipulation in the lab compared to its potential expression in the field. we focused on photoperiod cues in l. inflata; other cues, correlated with an unknown factor germane to expectation of realized reproductive effort, may influence the developmental decision to defer resources for a sre. finally, we note that our study was designed to test the adaptive deferral hypothesis, and rejection of this hypothesis does not conclusively establish that sres are maladaptive or nonadaptive in l. inflata. further study of sre expression in l. inflata elsewhere in its range would allow us to better assess the fitness consequences for plants expressing sres.  in conclusion, we found that while l. inflata plants had the ability to produce viable seeds in sre fruits, the pattern in which they did so was inconsistent with the adaptively plastic deferral of reproductive effort seen in animal systems: here, time-constraining primary reproduction resulted in semelparity with reduced secondary reproduction. this norm of reaction is consistent with the expression of vestigial iteroparity that decreases as time constraints increase. where seasonality is strong and winter is long, sres likely represent a loss of reproductive effort. thus, secondary reproductive episodes in l. inflata appear to be a vestige of their iteroparous evolutionary past. 
secondary reproduction has been explained as the adaptive deferral of reproductive potential under circumstances in which some fraction of reproductive success would otherwise have been lost. this deferral hypothesis predicts a positive relationship between constraints on primary reproduction and expression of secondary reproduction. although semelparity is a life history characterized by a single reproductive episode within a single reproductive season, some semelparous organisms facultatively express a second bout of reproduction, either in a subsequent season or later within the same season as the primary bout. our results were found to be inconsistent with the adaptive deferral explanation: first, plants whose primary reproduction was time-constrained exhibited decreased allocation to subsequent secondary reproduction, a result that was consistent across all three years; second, secondary offspring—although viable in the laboratory—would not have the opportunity for expression under field conditions, and would thus not contribute to reproductive success. although alternative adaptive explanations for secondary reproduction cannot be precluded, we conclude that the characteristics of secondary reproduction found in l. inflata are consistent with predictions of incomplete or transitional evolution to annual semelparity. here, we experimentally manipulate effective season length in each of three years to test whether secondary reproduction is a form of adaptive plasticity consistent with the deferral hypothesis. however, it is unknown whether secondary reproduction is an example of adaptive reproductive deferral, or is more parsimoniously explained as the vestigial expression of iteroparity after a recent transition to semelparity.
 although semelparity is a life history characterized by a single reproductive episode within a single reproductive season, some semelparous organisms facultatively express a second bout of reproduction, either in a subsequent season or later within the same season as the primary bout. secondary reproduction has been explained as the adaptive deferral of reproductive potential under circumstances in which some fraction of reproductive success would otherwise have been lost. this deferral hypothesis predicts a positive relationship between constraints on primary reproduction and expression of secondary reproduction. the herbaceous monocarp lobelia inflata has been observed occasionally to express a secondary reproductive episode in the field. however, it is unknown whether secondary reproduction is an example of adaptive reproductive deferral, or is more parsimoniously explained as the vestigial expression of iteroparity after a recent transition to semelparity. here, we experimentally manipulate effective season length in each of three years to test whether secondary reproduction is a form of adaptive plasticity consistent with the deferral hypothesis.  our results were found to be inconsistent with the adaptive deferral explanation: first, plants whose primary reproduction was time-constrained exhibited decreased allocation to subsequent secondary reproduction, a result that was consistent across all three years; second, secondary offspring—although viable in the laboratory—would not have the opportunity for expression under field conditions, and would thus not contribute to reproductive success.  although alternative adaptive explanations for secondary reproduction cannot be precluded, we conclude that the characteristics of secondary reproduction found in l. inflata are consistent with predictions of incomplete or transitional evolution to annual semelparity. life-history evolutionsemelparityiteroparityfacultative iteroparitylobelia inflata 