Reduction of a visually mediated association preference in the Cave molly ( Michael Tobler(1,2), Heike Burmeister(3), Ingo Schlup (2,3), Martin Plath Poecilia mexicana, Poeciliidae, Teleostei)

2006 Several studies have reported on the persistence of visually mediated social preferences, such as preferences of females to associate with certain types of males, in an eyed cave fish, the Cave molly (Poecilia mexicana). However, so far most studies have examined preferences which are apparently currently under selection, i.e., the preferences are expressed also in darkness. In this paper we examined female preferences for (1) conspecific females and (2) males without a parasite-induced color change (black spot disease, BSD). In both cases, selection on the persistence of the preference is not apparent. As predicted, surface-dwelling females preferred conspecific over heterospecific females, but this preference was not found in the Cave molly. However, we found no evidence for female preferences relative to BSD-infection of males. We discuss that BSD-resistance probably has a low indicator value, so that this trait appears to be of minor importance for female mate choice even in surface-dwelling mollies.

Patterns of speciation in endemic Mexican Goodeid fish: sexual conflict or early radiation? M. G. RITCHIE, S. A. WEBB, J. A. GRAVES, A. E. MAGURRAN & C. MACIAS GARCIA 2005  Currently there is much interest in the potential for sexual selection or conflict to drive speciation. Theory proposes that speciation will be accelerated where sexual conflict is strong, particularly if females are ahead because mate choice will accentuate divergence by limiting gene flow. The Goodeinae are a monophyletic group of endemic Mexican fishes with an origin at least as old as the Miocene. Sexual selection is important in the Goodeinae and there is substantial interspecific variability in body morphology, which influences mate choice, allowing inference of the importance of female mate choice. We therefore used this group to test the relationship between sexual dimorphism and speciation rate. We quantified interspecific variation in sexual dimorphism amongst 25 species using a multivariate measure of total morphological differentiation between the sexes that accurately reflects sexual dimorphism driven by female mate choice and also used a mtDNA-based phylogeny to examine speciation rates. Comparative analyses failed to support a significant association between sexual dimorphism and speciation rate. In addition, variation in the time course of speciation throughout the whole clade was also examined using a similar tree containing 34 extant species. A constant rates model for the growth of this clade was rejected, but analyses instead indicated a decline in the rate of speciation over time. These results support the hypothesis of an early expansion of the group, perhaps due to an early radiation influenced by the key innovation of live bearing, or the prevalence of Miocene volcanism. In general, support for the role of sexual selection in generating patterns of speciation is proving equivocal and we argue that vicariance biogeography and adaptive radiations remain the most likely determinants of major patterns of diversification of continental organisms.

Genetics of Platypoecilus III.  Inheritance of sex and crossing over of the sex chromosomes in the platyfish MYRON GORDON February 5, 1937 GENETIC evidence of crossing over between the sex G chromosomes of heterogametic individuals (XU males and WZ females) is so rare in animals as to give special significance to additional data on this occurrence.  AIDA (1921) has shown in the Japanese ricefield killifish, Aplocheilus, that the X and Y chromosomes of the male occasionally cross over. In 1930 he presented additional data on this, together with some interesting data involving aberrant sex ratios, which he interpreted as due to nondisjunction.

Modularity as a Fish (Xenotoca eiseni) Views It: Conjoining Geometric and Nongeometric Information for Spatial Reorientation Valeria Anna Sovrano and Angelo Bisazza, 2003 When disoriented in a closed rectangular tank, fish (Xenotoca eiseni) reoriented in accord with thelarge-scale shape of the environment, but they were also able to conjoin geometric information with nongeometric properties such as the color of a wall or the features provided by panels located at the corners of the tank. Fish encoded geometric information even when featural information sufficed to solve the spatial task. When tested after transformations that altered the original arrangement of the panels, fish were more affected by those transformations that modified the geometric relationship between the target and the shape of the environment.