Colour dimorphism in labrid fishes as an adaptation to life on coral reefs

Conspicuous coloration displayed by animals that express sexual colour dimorphism is generally explained as an adaptation to sexual selection, yet the interactions and relative effects of selective forces influencing colour dimorphism are largely unknown. Qualitatively, colour dimorphism appears more pronounced in marine fishes that live on coral reefs where traits associated with strong sexual selection are purportedly more common. Using phylogenetic comparative analysis, we show that wrasses and parrotfishes exclusive to coral reefs are the most colour dimorphic, but surprisingly, the effect of habitat is not influenced by traits associated with strong sexual selection. Rather, habitat-specific selective forces, including clear water and structural refuge, promote the evolution of pronounced colour dimorphism that manifests colours less likely to be displayed in other habitats. Our results demonstrate that environmental context ultimately determines the evolution of conspicuous coloration in colour-dimorphic labrid fishes, despite other influential selective forces.

Sexual Dimorphism in Erpetoicthys calabaricus from a Mangrove Creek, Nigeria

Sexual dimorphism of E. calabaricus is presented based on the examination of external morphology of the fish. Females had very pointed anal fins which joined the caudal fin smoothly with fewer than 10 spikes. Males had broader anal fin clearly separated from the caudal fin with between 9 and 12 spikes on the fin. Colour dimorphism in males tended towards an olive green, whereas the females had a light yellow-brown colour. Paired t-test showed that active females were slightly heavier than similarly-sized males. Length frequency distribution showed the largest fish was 39.9 cm TL female, while the smallest fish (TLmin) was 21 cm TL male. Sex ratio was in favour of males giving a male: female ratio of 1: 0.79 which was different from the expected 1: 1 ratio (χ2 = 9.110, df = 1, p < 0.05). The smallest female and male were 21.7 cm and 21 cm TL, thus delineating minimum sizes in the population. Largest female and male fishes measured 39.9 cm and 39.7 cm TL. Median sizes were 28.0 cm (females) and 29.0 cm (males).

New species reveal unexpected interspecific microhabitat diversity in the genus Uthina Simon, 1893 (Araneae : Pholcidae)

Representatives of the Southeast Asian pholcid spider genus Uthina Simon, 1893 have been thought to be very homogeneous in their ecology and morphology. The 14 previously known species all inhabit near-ground microhabitats and cave entrances, and range from pale to dark brown in colour. Even their genitalia are partly very similar, with some species pairs being barely distinguishable based on morphological characters. Here we describe three new species from Bali, Java and Sulawesi that represent three further microhabitats and demonstrate considerable ecological and morphological diversity within the genus: U. maya, sp. nov. from Bali is a large dark species on tree trunks; U. hylobatea, sp. nov. from Bali and eastern Java is a pale leaf-dwelling species that exhibits colour dimorphism; and U. mimpi, sp. nov. is a pale troglomorphic species collected in the aphotic zones of two South Sulawesi caves. In addition, we present new data for five previously described species, including ultrastructure, natural history, new records, taxonomic notes and a description of the previously unknown female of Uthina khaosokensis Yao, Li &amp; Jäger, 2014. Molecular data suggest that all previously described species are very closely related to each other (constituting the monophyletic luzonica-group), and that the three new species represent separate clades within the genus. However, the basal trichotomy could not be resolved: U. maya + (U. hylobatea + U. mimpi) + luzonica-group.

Patterns of phenotypic variation reveal substantial differentiation in sexual dimorphism of three Psammodromus (Squamata, Lacertidae) species

The Spanish sand racer (Psammodromus hispanicus) has been recently split into three distinct species: P. hispanicus, P. edwardsianus, and P. occidentalis. Some morphological differences have been reported but there is as yet no description allowing unambiguous identification of the three species. Here, we describe differentiation in body measurements, scalation traits, and colour traits as well as in the degree of sexual dimorphism. Our results show that P. edwardsianus can be easily distinguished by the presence of a supralabial scale below the subocular scale, which is absent in the other two species. Psammodromus hispanicus and P. occidentalis can be distinguished by the number of femoral pores, throat scales and ocelli, and the relative width of the anal scale. The degree of sexual size dimorphism and sexual colour dimorphism substantially differs among species, suggesting that different scenarios of sexual and natural selection may exist for each species. Moreover, sexually selected traits (nuptial colouration, ocelli, and femoral pores) significantly differ among species, suggesting that visual and chemical communication may also differ among species. Such differences could prevent reproduction and gene flow at secondary contact zones, potentially reinforcing isolation and speciation within this group of lizards.