No abstract

Variation in pigmentation traits is an effective window to evolutionary processes due to their importance for survival and reproduction. In particular, one of the leading hypotheses for the maintenance of conspicuous pigmentation in natural populations is its signaling function in mate choice. Here, we demonstrate the occurrence of melanism in poeciliid fishes of the genus Poecilia that inhabits toxic, hydrogen sulfide springs in southern Mexico and the absence of melanism from closely related populations in reference habitats lacking hydrogen sulfide. Assays of female mate preference in both habitat types were used to examine whether divergence in female preference for melanism contributes to its maintenance in hydrogen sulfide springs. We found significant variation in female preferences for melanistic males. Specifically, melanistic females from the toxic spring exhibited a significant preference for melanistic males, while non‐melanistic females from the same population exhibited no preference. Females from the non‐sulfidic reference population discriminated strongly against melanistic males. Preferences of melanistic females appear to be a significant force in the maintenance of melanism in sulfidic habitats and suggest a change in preference as the divergence from non‐sulfidic ancestors. Potential polymorphism in preference within the hydrogen sulfide spring indicates that preference for melanistic males may not be environmentally controlled. Thus, a change in preference following divergence can promote the maintenance of variation in pigmentation within populations and between divergent habitats.

Specimens of Xiphophorus birchmanni (Teleostei: Poeciliidae) (55 individuals) (Sheepshead swordtail) were collected from 2 localities in the Pánuco River drainage from Hidalgo and Veracruz [at Atlatipa (n = 26) and Benito Juárez (n = 29), respectively], México. The structure of the parasite communities of fish from the 2 localities was examined and compared. Helminths from 10 taxa were recovered: 6 species of larval digeneans (Posthodiplostomum sp., Uvulifer sp., Centrocestus formosanus, Ascocotyle sp., Haplorchis pumilio, and Echinostomatidae gen. sp.); 2 adult monogeneans (Urocleidoides vaginoclastrum and Gyrodactylus sp.); 1 larval cestode (metacestode stage; Glossocercus auritus); and 1 larval nematode, Eustrongylides sp. Urocleidoides vaginoclastrum and C. formosanus were the most frequent and abundant species. The remaining taxa were rare and found at low mean abundance. Component community and infracommunity differences observed in this study could be attributed to abiotic and biotic environmental factors resulting from the geographic separation of these localities during the orogeny of the Sierra Madre Oriental that restricted fish to isolated localities.

A total of 141 highland swordtails, Xiphophorus malinche, were collected from 2 localities in the Pánuco river drainage (Chicayotla and Malila) from Hidalgo, México. The parasite community structure of the 2 localities was examined and compared. Five taxa of helminths were recovered: 2 digeneans, adults of Paracreptotrema sp. and metacercariae of Uvulifer sp.; an adult monogenean, Urocleidoides vaginoclastrum; an adult cestode, Bothriocephalus acheilognathi, and an adult nematode, Rhabdochona xiphophori. Among them, Ur. vaginoclastrum was the most frequent and abundant species. The remaining species were rare and found at low mean abundance. Only 2 species of helminth were found at both localities. The observed species richness, individual abundance, and diversity were low at component community and infracommunity levels. Abundance of helminths and fish standard length were correlated. Uvulifer sp. was more abundant in small fish, but Ur. vaginoclastrum showed the opposite pattern, high abundance in larger fish. Differences observed in this study can be attributed to abiotic and biotic environmental factors resulting from the geographic separation of these localities during to the orogeny of the Sierra Madre Oriental that restricted fish to isolated headwaters.