Samuel Cotton’s research while affiliated with University College London and other places

A new species of Teleopsis (Diptera, Diopsidae) from Chiang Mai, Thailand is described and illustrated. Teleopsis thaii Földvári & Carr is shown to be a member of a species group, termed the dalmanni species group, along with three previ-ously described species. Presented here are a morphological description of T. thaii and an allometric comparison of the species with other members of the Teleopsis genus. We also present multi-gene phylogenetic analyses to highlight the possible position of T. thaii within the dalmanni species group.

A new species of Teleopsis (Diptera, Diopsidae) from Chiang Mai, Thailand is described and illustrated. Teleopsis thaii Földvári & Carr is shown to be a member of a species group, termed the dalmanni species group, along with three previously described species. Presented here are a morphological description of T. thaii and an allometric comparison of the species with other members of the Teleopsis genus. We also present multi-gene phylogenetic analyses to highlight the possible position of T. thaii within the dalmanni species group.

To control introduced exotic species that have predominantly genetic, but environmentally reversible, sex determination (e.g. many species of fish), Gutierrez and Teem recently modeled the use of carriers of Trojan Y chromosomes--individuals who are phenotypically sex reversed from their genotype. Repeated introduction of YY females into wild populations should produce extreme male-biased sex ratios and eventual elimination of XX females, thus leading to population extinction. Analogous dynamics are expected in systems in which sex determination is influenced by one or a few major genes on autosomes.

The 'lek paradox'--the hypothesis that females do not gain substantial genetic benefits from mate choice--could be resolved by sexually selected traits being indicative of male condition. A recent paper, however, suggests that this may not be the case in Drosophila bunnanda.

A long-standing problem in evolutionary biology is whether females derive genetic benefits from mating with well-ornamented males. Male sexual ornaments are believed to be informative signals of male genetic quality as they exhibit condition-dependent expression, with condition being influenced by many loci in a male's genome. But persistent selection on ornaments and condition should cause genetic variation in male fitness to be depleted rapidly, thereby eliminating any advantage to female mate preference – a problem known as the 'lek paradox'. Recently, Petrie and Roberts (2006) proposed that female mate choice indirectly selects for elevated rates of mutation, and claim this increases the amount of available genetic variation faster than sexual selection can erode it. Their solution provides an intriguing resolution to the lek paradox, but can it really account for the maintenance of genetic variation in fitness associated with sexual ornaments?

The last decade has witnessed considerable theoretical and empirical investigation of how male sexual ornaments evolve. This strong male-biased perspective has resulted in the relative neglect of variation in female mate preferences and its consequences for ornament evolution. As sexual selection is a co-evolutionary process between males and females, ignoring variation in females overlooks a key aspect of this process. Here, we review the empirical evidence that female mate preferences, like male ornaments, are condition dependent. We show accumulating support for the hypothesis that high quality females show the strongest mate preference. Nonetheless, this is still an infant field, and we highlight areas in need of more research, both theoretical and empirical. We also examine some of the wider implications of condition-dependent mating decisions and their effect on the strength of sexual selection.

A new species of Diasemopsis (Diptera, Diopsidae) from Comoro Islands is described and illustrated for the first time with allometric datasets. Diasemopsis comoroensis Carr & Földvári is shown to be genetically close, but morphologically distinct from the widespread Afro-tropical species D. meigenii (Westwood); notably a significant divergence in the degree of sexual dimorphism within eye span has occurred between the two species. A revised molecular phylogeny of the genus Diasemopsis is presented based on the partial sequences of four genes.

A new specie s of Diasemopsis (Diptera, Diopsidae ) from Comoro Islands is described and illustrated for the first time wi th a llometric datasets . Diasemopsis comoroensis Carr & Földvár i is shown t o be genetically close, but morphologically distinct from th e widesprea d Afro-tropical species D. meigenii (Westwood); notably a significant dive rgence in the degree of sexual dimorphism within eye spa n has occurre d between the two species. A revised molecula r phylogeny of th e genus Diasemopsis is presente d based on the partial sequenc es of four genes.

There is currently much interest in mate preferences for sexual ornaments. However, few studies have focused on individual variation in mate preference despite its importance for the rate and direction of sexual selection. Females of the sexually dimorphic stalk-eyed fly, Diasemopsis meigenii, exhibit an unambiguous rejection response towards unattractive males bearing small ornaments. We investigated individual mate preferences using repeated sequential sampling of female rejection or acceptance responses to a wide range of male ornament phenotypes. We found significant variation in the strength of individual preference. In addition, preference was positively associated with female eyespan, a condition-dependent trait putatively linked to visual acuity.

In stalk-eyed flies (Diopsidae) the eyes and antennae are laterally displaced at the ends of elongated eyestalks. Eyespan and the degree of sexual dimorphism in eyespan vary considerably between species and several sexually dimorphic species show sexual selection through female mate preference for males with exaggerated eyespan. The genes on which selection acts to regulate eyespan remain to be identified. This could be achieved by comparing gene expression during eyestalk development in males and females if the sex of pre-adult flies could be reliably assigned. Here we describe two techniques, one morphological and one microsatellite-based, that identify the sex of stalk-eyed fly larvae and pupae. We showed that genital discs of the stalk-eyed fly Teleopsis dalmanni have two highly distinct morphologies, compact ("C") and lobed ("L"). Segment composition (revealed by Engrailed expression) was consistent with C morphology being typical of males and L morphology of females. We confirmed the proposed association between disc morphology and sex by evaluating the combined heterozygosity of four X-linked microsatellite markers. We demonstrated that individuals with C genital discs had hemizygous (male) genotypes while those with L discs were heterozygous (female) genotypes. Similar dimorphism in genital disc morphology was observed in eight other species spanning three representative Diopsid genera. In every case the segment composition supported C morphology being male and L morphology female. We assigned larval sex by C or L morphology and compared cell division frequencies in male and female eye-antennal discs in two species (T. dalmanni and Diasemopsis meigenii) sexually dimorphic for eyespan. The number of mitotic (anti-H3-labelled) cells did not differ between the sexes in either species. We have made novel use of two complementary techniques for identifying the sex of pre-adult stalk-eyed flies. These procedures will facilitate studies of the evolution of sexually dimorphic development in a variety of other species. Morphology and En expression in male and female genital discs are highly conserved within each genus of Diopsidae. Finally, sexual dimorphism for eyespan in two Diopsid species is unlikely to be due to an increased rate of cell division at the third larval instar in males.