Sexual selection, mating system and ecology of the Wellington tree weta (Hemideina crassidens).
Published: 2005
Language: eng
Number of pages: 349
Description: In this dissertation I investigate how sexual selection has driven the evolution of a sexually dimorphic character in an orthopteran insect, the Wellington tree weta, Hemideina crassidens (Ensifera: Anostostomatidae).Tree weta have long been thought of as a resource-defence animal in which single adult males control cavities in trees (hereafter galleries) which are used by sexually receptive females for refuge. This provides males with sole access to one or more mates. I first examined the theoretical and empirical support for a number of hypotheses related to the resource-defence role mating system by synthesizing the relevant literature on insects with this type of mating system. Although many insect species exhibit resource-defence and several studies have been conducted on such animals, our knowledge of the resource-defence mating system remains poor. That is, we know some aspects of the behavioural ecology of many resource-defence insects but few species have been studied in-depth.I found that the opportunity for sexual selection (I mates) is high in habitats with small galleries but low in large galleries. This pattern was opposite to prediction and arises because, in small galleries, there is a large proportional difference between those males that have a harem versus those males that are single whereas in large galleries a greater proportion of males reside with a female(s). The strength of sexual selection (selection gradients) on male weaponry was as predicted and opposite to the pattern observed for opportunity for selection. That is, larger weaponry was favoured in large galleries whereas smaller weaponry was favoured in smaller galleries. I hypothesize that this pattern results from selection favouring greater mobility in smaller galleries because smaller galleries house smaller harems and so for a male to maximize fitness, he should visit more galleries per unit time compared with males in larger galleries. Selection likely favours larger weaponry in large galleries because males require greater resource-holding potential (i.e. fighting ability) to maintain control of the larger harems housed in large galleries. (Abstract shortened by UMI.)I used both laboratory and field as well as cross-sectional and longitudinal approaches to investigate how sexual selection drives the evolution of sexual dimorphism and to show that H. crassidens exhibits a male dominance polygynandrous mating system, and not resource-defence. I showed that the Wellington tree weta is sexually dimorphic with males possessing positively allometric mandibles which are used as weapons in fights for groups of females (hereafter harems) in galleries. These weapons exhibit a multimodal size distribution and harem success is positively correlated with weapon size presumably because males with larger mandibles are more successful in male-male combat.
Notes: Source: Dissertation Abstracts International, Volume: 66-10, Section: B, page: 5270.

Thesis (Ph.D.)--University of Toronto, 2005.

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