DOI: 10.5061/dryad.x69p8czs3
title: Pollen interference between rare and common species

description: The mechanisms underlying plant species distribution and abundance have
 been long studied in ecology. However, the role of heterospecific pollen
 interference in shaping these patterns remains unaddressed. Species
 distribution and abundance are important factors determining whether a
 species is endangered or not, thus understanding the impact of
 heterospecific pollen interference on rare species could help to inform
 conservation strategies aimed at preserving plant communities. In this
 study, we conducted a multispecies experiment using eight co-occurring and
 co-flowering plant species with varying rarity levels in Switzerland. We
 performed hand-pollination experiments between all species pairs and
 measured seed set (whether a flower produces seed) and seed number (number
 of seeds per flower) as outcomes. We looked at the effects of species
 rarity status, species self-compatibility and recipient-donor relatedness
 on heterospecific pollen interference. Contrary to expectations, neither
 seed set nor seed number were affected by heterospecific pollen
 deposition. Self-compatible species had a higher seed set probability, but
 this was independent from species rarity. Lastly, rare species showed a
 decrease in heterospecific pollen interference with more distantly related
 pollen donors when these were rare as well. In our study setting,
 heterospecific pollen interference seems to have only minor effects on
 seed set and seed number, and consequently on recruitment. Thus,
 heterospecific pollen interference seems to play only a minor role in
 shaping plant species distribution and abundance. Nevertheless, the higher
 impact of heterospecific pollen deposition for rare and closely related
 species might need further investigation for both in-situ and ex-situ
 conservation strategies.
description: Species used We used a total of eight species
 with different distribution and IUCN red list status within Switzerland.
 All species are co-occurring in the lime-rich crop fields habitat
 (“Caucalidion” according to the classification by Delarze, Gonseth,
 Eggenberg, & Vust, 2015), insect-pollinated and have overlapping
 flowering times in nature (Landolt et al., 2010; Lauber, Wagner, &
 Gygax, 2018). We classified species as “common” if their IUCN status in
 Switzerland was “least concern”, and as rare otherwise. IUCN status in
 Switzerland correlated strongly with number of observation within
 Switzerland pooled between the years 2000 and 2020 (cor: 0.86, p-value
 &lt; 2.2*10-16). Breeding system (self-compatible vs
 self-incompatible) was extracted from the BioFlor database (Kuehn, Durka,
 & Klotz, 2004). To test the relationship between recipient-donor
 relatedness and heterospecific pollen interference, we constructed a
 phylogenetic tree for our species by pruning a modified version (Malecore,
 Dawson, Kempel, Müller, & van Kleunen, 2018) of the dated DaPhnE
 supertree of Central European plant species (Durka & Michalski,
 2012) and then calculated the phylogenetic distance using the cophenetic
 function of the “ape” package (Paradis, E. Claude & Strimmer,
 2004) in R. <br>Experimental set-up
 We sowed all species into 12 cm x 17 cm trays filled with
 Seedling substrate (Klasmann-Deilmann GmbH, 49741 Geeste, Germany) and put
 them into the dark coolroom at -4°C for stratification between 5 and 8
 weeks. Once seeds would start to germinate, we moved the trays to a
 greenhouse compartment. We transplanted seedlings into 11 cm x 11 cm x 12
 cm pots filled with Selmaterra (fertilized heavy soil with 30% volume
 peat, see Table S 2). We randomized pots on tables of a single greenhouse
 compartment and watered as well as fertilized regularly. We treated aphids
 and fungi whenever necessary. All species flowered
 between May 2021 and October 2021. To assure continuing of flowering, we
 regularly cut untreated flowers. To assess the effect size of
 heterospecific pollen interference, we performed hand pollinations among
 all species and measured seed set (yes/no) and seed number (counts). For
 the heterospecific pollen treatment, we prepared a saturated mix of
 conspecific pollen and heterospecific pollen and applied it to the stigma
 of the recipient flower. For each flower treated with heterospecific
 pollen mixture, we treated a second flower on the same plant individual on
 the same day with conspecific pollen only as a control, using the same
 conspecific pollen donor that we used for the heterospecific pollen mix.
 The two flowers with heterospecific and conspecific treatment would
 constitute a pair with the same “pair ID”. Pollen grain number per anther
 differed greatly depending on individual and on anther ripeness, thus we
 standardized treatment by always applying a pollen amount above saturation
 level. We extracted the pollen for the treatments from the anthers by
 tapping them on a glass slide and with the help of tweezers, and then
 mixed it for the heterospecific treatment using tweezers. We then applied
 the pollen mixture (HP) or the conspecific pollen (CP) to the open stigma
 of the recipient flower. To avoid selfing, we emasculated recipient
 flowers by removing the anthers some days before treatment. For some
 species (Bupleurum rotundifolium, Fallopia convolvulus, Myosotis
 arvensis), anther removal would cause too much flower damage due to the
 small size, thus anthers were not removed. For these species, selfing
 could not be completely excluded. For each
 donor-recipient combination, we treated between 2 and 16 flower pairs (HP
 and CP; median: 12 flower pairs per donor-recipient combination). We
 collected seeds after ripening, and counted them either by hand or by
 using an imaging method with imageJ (Abramoff, Magalhaes, & Ram,
 2004).
description: Data from multispecies greenhouse experiment where conspecific pollination
 and heterospecific pollination were performed between eight species with
 different rarity in Switzerland, to assess heterospecific pollen
 interference. All eight species belong to the habitat type
 "Caucalidion". Species were grown in the greenhouse from seeds
 collected in the wild and treated once they started to flower. Seeds
 produced were counted as outcome variable. Treatments: For the
 heterospecific pollen treatment, we prepared a saturated mix of
 conspecific pollen and heterospecific pollen and applied it to the stigma
 of the recipient flower. For each flower treated with heterospecific
 pollen mixture, we treated a second flower on the same plant individual on
 the same day with conspecific pollen only as a control, using the same
 conspecific pollen donor that we used for the heterospecific pollen mix.
 The two flowers with heterospecific and conspecific treatment would
 constitute a pair with the same “pair ID”. We standardized treatment by
 always applying a pollen amount above saturation level. We extracted the
 pollen for the treatments from the anthers by tapping them on a glass
 slide and with the help of tweezers, and then mixed it for the
 heterospecific treatment using tweezers. We then applied the pollen
 mixture (HP) or the conspecific pollen (CP) to the open stigma of the
 recipient flower. To avoid selfing, we emasculated recipient flowers by
 removing the anthers some days before treatment. For some species
 (Bupleurum rotundifolium, Fallopia convolvulus, Myosotis arvensis), anther
 removal would cause too much flower damage due to the small size, thus
 anthers were not removed. For these species, selfing could not be
 completely excluded. For each donor-recipient combination, we treated
 between 2 and 16 flower pairs (HP and CP; median: 12 flower pairs per
 donor-recipient combination). We collected seeds after ripening, and
 counted them either by hand or by using an imaging method with imageJ
 (Abramoff, Magalhaes, & Ram, 2004) ## Description of the data and file
 structure \# Recipient : Genus_species of the recipient; 8 species used
 (Ajuga_chamaepitys, Bupleurum_rotundifolium, Consolida_regalis,
 Fallopia_convolvulus, Iberis_amara, Myosotis_arvensis, Nigella_arvensis,
 Papaver_rhoeas,). \# Recipient.ID : ID of the plant individual of a given
 species. \# Flower.ID : ID of the flower within a plant individual. \#
 Type : Treatment type - conspecific CP, heterospecific HP, selfing SF. \#
 DonorHP : HP donor Genus_species. \# DonorHP.ID : HP donor
 Genus_species_ID; "NO" for "CP" and "SF"
 treatment types. \# DonorCP.ID : CP donor Genus_species_ID; same as the
 recipient ID for "SF" treatment type. \# Treatment.date :
 Treatment date (day/month/year). \# Pair.ID : Unique ID for each pair;
 each HP or SF is associated with a conspecific control in a pair. \#
 Recipient.IUCN : IUCN status of Recipient in CH. \# Recipient.WA.IUCN :
 IUCN status of Recipient in Westliche Zentralalpen, roughly overlapping
 with Wallis. \# Recipient.endangered: Dichotomous variable for Recipient;
 0 when IUCN status LC, 1 in all other cases. \# Donor.IUCN : IUCN status
 of Donor in CH. \# Donor.WA.IUCN : IUCN status of Donor in Westliche
 Zentralalpen, roughly overlapping with Wallis. \# Donor.endangered :
 Dichotomous variable for Donor; 0 when IUCN status LC, 1 in all other
 cases. \# PD : Phylogenetic distance Recipient-Donor (from Daphne tree).
 \# Seed.counts : Seed number; integer. ## Sharing/Access information NA ##
 Code/Software NA