Research

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Research

Alternative Reproductive Tactics

Condition-dependence

Positive Allometry

Phenotypic Plasticity

Integration and Compensation

Female Choice and Genetic Variation

Developmental Instability

The evolution of alternative reproductive tactics

I have recently been collaborating with Wade Hazel, a pioneer of quantitative genetic models of the conditional strategy, and have reviewed the status of the conditional evolutionarily stable strategy, advocating a quantitative genetic approach. I am interested in testing these theoretical models of the evolution of male ‘threshold’ traits, principally using earwigs (Dermaptera), dung beetles (Coleoptera) and mites (Acari) as model systems. These systems generate insights into sexual selection in the field, the allometry of dimorphic expression and lab evolution of threshold characters respectively. [top]

The European earwig (Forficula auricularia)

I have been studying the European earwig F. auricularia since 1993. This species is common in the United Kingdom, but relatively poorly understood. I am particularly interested in the species because it has a male dimorphism in forceps length. The unusual feature of the dimorphism is that it shows extraordinary local variation in expression, some populations are monomorphic, while others close by are dimorphic. These earwigs provide an opportunity to study the evolution of male dimorphic threshold traits in the field, and the focus of my research is on the evolution of the forceps length dimorphism in UK island populations. This involves a population genetic approach to understanding the phylogeography of island and mainland variation in forceps morphology. In addition I have quantified the environmental parameters that are likely to influence selection on alternative male tactics (Tomkins and Brown 2004). These approaches are accompanied by estimates of sexual selection in the field from across a range of island populations. [top]

The Acarid mite Sancassania berlesei

I am collaborating with Dr Jacek Radwan and Dr Natasha LeBas on the evolutionary genetics of the male dimorphism in the Acarid mite Sancassania berlesei. In this species males are either ‘fighters’ and have a specialised third-pairs of legs that are used for fighting or are ‘scramblers’ and have unmodified legs. This is a dichotomous dimorphism that is status dependent. We have shown that the threshold expression of male morphs in this species is itself phenotypically plastic in response to density. Our research currently focuses on how populations diverge in the expression of threshold traits and in the quantification of fitness functions of alternative tactics in this species. [top]

The dung beetle Onthophagus taurus

Onthophagus taurus is a dung beetle that exhibits a dramatic horn length dimorphism. During my first fellowships here at the University of Western Australia I collaborated with Leigh Simmons and colleagues Janne Kotiaho, and John Hunt on sperm competition in these beetles and on the quantitative genetics of condition and the male horn length dimorphism. In collaboration with Natasha LeBas and Janne Kotiaho, we have been using O. taurus to investigate positive allometry and the evolution of male dimorphic traits. [top]

Condition and condition-dependence in sexual selection

The concept of ‘condition’ is widely used but poorly understood. Primarily the use of condition has been as a phenotypic character; however I am interested in identifying the genetic basis of condition as a means of gaining greater understanding of its properties. Research on condition and condition dependence forms the basis of my current ARC Fellowship. The genetic properties of condition have stimulated my interest in the interplay between condition-dependence and adaptation. [top]

Positive allometry and sexual selection

Allometry is the study of the proportionality of organs, traits, or investment. I am interested in the allometry of primary and secondary sexual traits. Measuring investment in such traits that does not account appropriately for allometry is prone to error, bringing these statistical issues to wider attention has been a recent goal (Hoysak and Tomkins in review; Tomkins and Simmons 2002). Research in collaboration with Rob Knell on the allometry of stag beetles jaws has demonstrated that in some of the more elaborate species the limits to elaboration have been met (Knell et al 2004). I have also been collaborating with Natasha LeBas and Janne Kotiaho on the allometric basis to male dimorphisms in dung beetles and earwigs. Our data show how positive allometry can play an important role in the dimorphic reaction norms present in the morphology of many insect species (Tomkins et al 2005). [top]

Phenotypic plasticity and secondary sexual trait compensation

We interested how organisms devote resources to structures that increase their reproductive success directly – secondary sexual traits – but also in the structures that support or facilitate such traits or displays. The compensation for elaborate structures like the horns of the dung beetle Onthophagus taurus requires some developmental integration between the display trait and the morphological traits that make display possible. Where organisms are dimorphic, this integration is likely to be plastic. We are investigating the phenotypic (Tomkins et al 2005) and genetic basis to this phenomenon in the dung beetle O. taurus and the European earwig Forficula auricularia. [top]

Female choice and the maintenance of additive genetic variance

A longstanding evolutionary question, that keeps scores of Behavioural Ecologists in a job, is how genetic variance in fitness related life-history traits is maintained under directional selection. I have been involved in empirical (Kotiaho et al 2000), theoretical (Colegrave et al) and review-orientated (Tomkins et al 2004) approaches to this subject. Currently, I am examining population variation in female choice and the quantitative genetic variation in secondary sexual traits in isolated island populations of the earwig Forficula auricularia. And, in collaboration with Dr Janne Kotiaho using the bean weevil Callosobruchus maculatus and Dr Jacek Radwan using S. berlesei, I am testing the genic-capture model of condition dependent trait expression using quantitative genetic techniques. [top]

The evolutionary significance of developmental instability

Fluctuating asymmetries are small deviations from bilateral symmetry that are found in otherwise symmetrical traits. Because symmetry is expected to be the ideal state, deviations from symmetry are thought to be evidence for developmental instability and thereby an individual’s genetic quality I have conducted comparative studies of the evolution of fluctuating asymmetry across species of earwigs (Tomkins and Simmons 1995) and in species with male dimorphisms (Tomkins and Simmons 1996). I have also investigated the heritability of asymmetry in earwig forceps (Tomkins and Simmons 1999) and hypothesis that individuals pay attention to asymmetries in the secondary sexual traits (forceps) of earwigs (Tomkins and Simmons 1999). I am also interested in the changes in effect size through time of studies addressing the hypothesis that FA is involved in sexual selection (Tomkins and Simmons 2003). I am currently furthering my investigations (Tomkins 1999) into the ontogeny of fluctuating asymmetries in hemimetabolous insects, and the relationship between phenodeviation and developmental instability. [top]