Courtship behavior in the knife livebearer Alfaro cultratus (Cyprinodontiformes: Poeciliidae).

The mating behavior of the knife livebearer Alfaro cultratus is described in detail. During "rubbing," the male swims to a position above the female and gently moves down repeatedly touching the dorsal part of female head with the pelvic fin tips. This courtship behavior constitutes the first report of a pelvic fin male-female contact during mating in poecilids. Based on preliminary evidence, I propose that a sensory bias mechanism could mediate the evolution of signal design/mate choice in this species, which should be tested in further studies.

Genetic and ecomorphological divergence between sympatric Astyanax morphs from Central America.

Intraspecific ecological and morphological polymorphism can promote ecological speciation and the build-up of reproductive isolation. Here, we evaluate correlations among morphology, trophic ecology and genetic differentiation between two divergent morphs (elongate and deep-body) of the fish genus Astyanax in the San Juan River basin in Central America, to infer the putative evolutionary mechanism shaping this system. We collected the two morphs from three water bodies and analysed: (1) the correlation between body shape and the shape of the premaxilla, a relevant trophic morphological structure, (2) the trophic level and niche width of each morph, (3) the correspondence between trophic level and body and premaxillary shape, and (4) the genetic differentiation between morphs using mitochondrial and nuclear markers. We found a strong correlation between the body and premaxillary shape of the morphs. The elongate-body morph had a streamlined body, a premaxilla with acuter angles and a narrower ascending process, and a higher trophic level, characteristic of species with predatorial habits. By contrast, the deep-body morph had a higher body depth, a premaxilla with less acute angles and a broader trophic niche, suggesting generalist habits. Despite the strong correlation between morphological and ecological divergence, the morphs showed limited genetic differentiation, supporting the idea that morphs may be undergoing incipient ecological speciation, although alternative scenarios such as stable polymorphism or plasticity should also be considered. This study provides support for the role of ecological factors promoting diversification in both lake and stream-dwelling freshwater fish.

A geographical cline in craniofacial morphology across populations of Mesoamerican lake-dwelling fishes.

Together, the complex geological history and climatic diversity of Mesoamerica create a rich source of biodiversity from which evolutionary processes can be studied. Here, we discuss highly divergent morphs of lake-dwelling fishes distributed across Mexico and Central America, originally recognized as members of different genera (Astyanax and "Bramocharax"). Recent phylogenetic studies, however, suggest these morphs group within the same genus and readily hybridize. Despite genetic similarities, Bramocharax morphs exhibit stark differences in cranial shape and dentition. We investigated the evolution of several cranial traits that vary across morphs collected from four lakes in Mexico and Nicaragua and discovered an ecomorphological cline from northern to southern lakes. Northern populations of sympatric morphs exhibit a similar cranial shape and tooth morphology. Southern populations of Bramocharax morphs, however, showed a larger disparity in maxillary teeth, length and frequency of unicuspid teeth, an elongated snout, and a streamlined cranium compared to Astyanax morphs. This divergence of craniofacial morphology likely evolved in association with differences in trophic niches. We discuss the morphological differences across the four lake systems in terms of geological history and trophic dynamics. In summary, our study suggests that Bramocharax morphs are likely locally adapted members derived from independent Astyanax lineages, highlighting an interesting parallel evolutionary pattern within the Astyanax genus.

Mating and aggressive behaviour of Brachyrhaphis olomina (Cyprinodontiformes: Poeciliidae).

Despite the increasing interest in the use of intromittent male genitalia and coercive mating behaviour in poeciliids, detailed studies of the mating behaviour of most species in this family are lacking. We describe here the mating and aggressive behaviours of Brachyrhaphis olomina, and correlate them with the condition of the female's ovum and embryos (immature, mature and pregnant). B. olomina performed a wide range of aggressive (sidle spread, tail beating, coordinate) and mating behaviours (approximation, touch, lateral display, touch-lateral display). Some behaviours (e.g. tail beating) are shared with other poeciliids, but two sexual behaviours (touch and lateral display) and one aggressive (coordinate) behaviour may be unique to B. olomina and were not reported in a previous study. Differences in male behaviour when paired with a female with mature ovum (more mating displays, no agonistic movements) suggest that males detect the female's reproductive condition from some distance. The distinctive nature of mating behaviour in B. olomina highlights the importance of studying different species to have a better understanding of the evolution of mating and aggressive behaviours in poeciliids. Digital video images related to the article are available at http://www.momo-p.com/showdetail-e.php?movieid=momo170720bo01a, http://www.momo-p.com/showdetail-e.php?movieid=momo170720bo02a and http://www.momo-p.com/showdetail-e.php?movieid=momo170720bo03a.

A new species of Roeboides (Teleostei: Characidae) from Costa Rica and Panama, with a key to the middle American species of the genus

A new species of Roeboides is described from the Pacific slope of Costa Rica and Panama. Roeboides bussingi differs from all other Central American Roeboides and all members of the R. guatemalensis species group by the following combination of characters: presence of 18-22 scales above the lateral line (vs. 12-16 in R. dientito); 15-22 scales below the lateral line (vs. 10-14 in R. dientito, and 20-24 in R. loftini); an inconspicuous, sometimes absent, crescent-shaped humeral spot (vs. a large round, conspicuous humeral spot in R. carti, R. dayi, R. dientonito, R. ilseae, R. loftini, and R. occidentalis); a small wedge-shaped spot that does not reach the lateral line (vs. a large spot crossing the lateral line in R. guatemalensis); a teardrop shaped caudal spot (vs. caudal spot triangle shaped in R. bouchellei); and a dark band at the distal tip of the anal fin (vs. dark band absent in R. bouchellei). A key to all Middle American species of Roeboides is also presented.

Uma espécie nova de Roeboides é descrita da vertente pacífica da Costa Rica e Panamá. Roeboides bussingi difere de todas as outras espécies de Roeboides da América Central e de todos os membros do grupo R. guatemalensis pela seguinte combinação de caracteres: presença de 18-22 escamas acima da linha lateral (vs. 12-16 em R. dientito); 15-22 escamas abaixo da linha lateral (vs. 10-14 em R. dientito e 20-24 em R. loftini); mancha umeral inconspícua, as vezes ausente, no formato de meia lua (vs. mancha humeral conspicua e arredondada em R. carti, R. dayi, R. dientonito, R. ilseae, R. loftini e R. occidentalis); pequena mancha em forma de cunha, não alcançando a linha lateral (vs. mancha grande, atravessando a linha lateral em R. guatemalensis); mancha do pedúnculo caudal em formato de gota d'água (vs. mancha caudal com formato triangular em R. bouchellei); banda escura na margem distal da nadadeira anal (vs. banda escura ausente em R. Bouchellei). Uma chave para todas as espécies de Roeboides da América Média é fornecida.