We investigated mechanisms of reproductive isolation in livebearing fishes (genus Poecilia) inhabiting sulfidic and nonsulfidic habitats in three replicate river drainages. Although sulfide spring fish convergently evolved divergent phenotypes, it was unclear if mechanisms of reproductive isolation also evolved convergently. Using microsatellites, we found strongly reduced gene flow between adjacent populations from different habitat types, suggesting that local adaptation to sulfidic habitats repeatedly caused the emergence of reproductive isolation. Reciprocal translocation experiments indicate strong selection against immigrants into sulfidic waters, but also variation among drainages in the strength of selection against immigrants into nonsulfidic waters.Mate choice experiments revealed the evolution of assortative mating preferences in females from nonsulfidic but not from sulfidic habitats. The inferred strength of sexual selection against immigrants (RI s ) was negatively correlated with the strength of natural selection (RI m ), a pattern that could be attributed to reinforcement, whereby natural selection strengthens behavioral isolation due to reduced hybrid fitness. Overall, reproductive isolation and genetic differentiation appear to be replicated and direct consequences of local adaptation to sulfide spring environments, but the relative contributions of different mechanisms of reproductive isolation vary across these evolutionarily independent replicates, highlighting both convergent and nonconvergent evolutionary trajectories of populations in each drainage.

The brain is a plastic organ, and so intraspecific studies that compare results obtained from wild individuals with those from common‐garden experiments are crucial for studies aiming to understand brain evolution. We compared volumes of brain regions between reproductively isolated populations of a neotropical fish, Poecilia mexicana, that has locally adapted to perpetual darkness (Cueva Luna Azufre), toxic hydrogen sulphide in a surface stream (El Azufre) or a combination of both stressors (Cueva del Azufre). Wild fish showed habitat‐dependent differences: enlarged telencephalic lobes and reduced optic tecta were found in fish living in darkness and sulphidic waters, in darkness without hydrogen sulphide or exposed to light and sulphide; fish from the sulphidic cave additionally showed enlarged cerebella. Comparison with common‐garden reared fish detected a general decrease in brain size throughout populations in the lab, and little of the brain size divergence between lab‐reared ecotypes that was seen in wild‐caught fish. The pronounced differences in brain region volumes between ecotypes in the wild might be interpreted within the framework of mosaic evolution; however, the outcomes of common‐garden experiments indicate a high amount of phenotypic plasticity. Our study thus highlights the importance of combining the investigation of brain size in wild populations with common‐garden experiments for answering questions of brain evolution.

The development of digestive enzymes during the early ontogeny of the Mayan cichlid (Cichlasoma urophthalmus) was studied using biochemical and electrophoretic techniques. From yolk absorption (6 days after hatching: dah), larvae were fed Artemia nauplii until 15 dah, afterward they were fed with commercial microparticulated trout food (45% protein and 16% lipids) from 16 to 60 dah. Several samples were collected including yolk-sac larvae (considered as day 1 after hatching) and specimens up to 60 dah. Most digestive enzymes were present from yolk absorption (5-6 dah), except for the specific acid proteases activity (pepsin-like), which increase rapidly from 8 dah up to 20 dah. Three alkaline proteases isoforms (24.0, 24.8, 84.5 kDa) were detected at 8 dah using SDS-PAGE zymogram, corresponding to trypsin, chymotrypsin and probably leucine aminopeptidase enzymes, and only one isoform was detected (relative electromobility, Rf = 0.54) for acid proteases (pepsin-like) from 3 dah onwards using PAGE zymogram. We concluded that C. urophthamus is a precocious fish with a great capacity to digest all kinds of food items, including artificial diets provided from 13 dah.

BackgroundIn many species males face a higher predation risk than females because males display elaborate traits that evolved under sexual selection, which may attract not only females but also predators. Females are, therefore, predicted to avoid such conspicuous males under predation risk. The present study was designed to investigate predator-induced changes of female mating preferences in Atlantic mollies (Poecilia mexicana). Males of this species show a pronounced polymorphism in body size and coloration, and females prefer large, colorful males in the absence of predators.ResultsIn dichotomous choice tests predator-naïve (lab-reared) females altered their initial preference for larger males in the presence of the cichlid Cichlasoma salvini, a natural predator of P. mexicana, and preferred small males instead. This effect was considerably weaker when females were confronted visually with the non-piscivorous cichlid Vieja bifasciata or the introduced non-piscivorous Nile tilapia (Oreochromis niloticus). In contrast, predator experienced (wild-caught) females did not respond to the same extent to the presence of a predator, most likely due to a learned ability to evaluate their predators' motivation to prey.ConclusionsOur study highlights that (a) predatory fish can have a profound influence on the expression of mating preferences of their prey (thus potentially affecting the strength of sexual selection), and females may alter their mate choice behavior strategically to reduce their own exposure to predators. (b) Prey species can evolve visual predator recognition mechanisms and alter their mate choice only when a natural predator is present. (c) Finally, experiential effects can play an important role, and prey species may learn to evaluate the motivational state of their predators.

Common snook (Centropomus undecimalis) is one of the most important marine species under commercial exploitation in the Gulf of Mexico; for this reason, interest in developing its culture is a priority. However, larviculture remains as the main bottleneck for massive production. In this sense, our objective was to determine the changes of digestive enzymes activities using biochemical and electrophoretic techniques during 36 days of Common snook larviculture fed with live preys (microalgae, rotifers, and Artemia). During larviculture, all digestive enzymatic activities were detected with low values since yolk absorption, 2 days after hatching (dah) onwards. However, the maximum values for alkaline protease (6,500 U mg protein(-1)), trypsin (0.053 mU × 10(-3) mg protein(-1)), and Leucine aminopeptidase (1.4 × 10(-3) mU mg protein(-1)) were detected at 12 dah; for chymotrypsin at 25 dah (3.8 × 10(-3) mU mg protein(-1)), for carboxypeptidase A (280 mU mg protein(-1)) and lipase at 36 dah (480 U mg protein(-1)), for α-amylase at 7 dah (1.5 U mg protein(-1)), for acid phosphatases at 34 dah (5.5 U mg protein(-1)), and finally for alkaline phosphatase at 25 dah (70 U mg protein(-1)). The alkaline protease zymogram showed two active bands, the first (26.3 kDa) at 25 dah onwards, and the second (51.6 kDa) at 36 dah. The acid protease zymogram showed two bands (RF = 0.32 and 0.51, respectively) at 34 dah. The digestive enzymatic ontogeny of C. undecimalis is very similar to other strictly marine carnivorous fish, and we suggest that weaning process should be started at 34 dah.

Several samples of P. splendida larvae were obtained from eggs until day 60 after hatching (dah) to determine acid and alkaline proteases, trypsin, chymotrypsin, leucine aminopeptidase, α-amylase, lipase, and acid and alkaline phosphatase activities using biochemical techniques. Additionally, SDS-PAGE alkaline protease zymogram and PAGE acid protease zymogram were carried out to identify active isoforms during larviculture. Alkaline protease and chymotrypsin were present at the moment of hatching, increased gradually reaching the maximum values at 35 dah. Trypsin and leucine aminopeptidase activities were low from hatching, increasing gradually as larvae grew. Alkaline protease zymogram showed four zymogens, which appears at different days, remaining present until the end of the larviculture (95.2 kDa at 11 dah, 26.4 kDa at 9 dah, 21.4 kDa at 3 dah, and 23.3 kDa at hatching). Pepsin activity was present at day 7 after hatching and increased progressively until the end of the larviculture. Acid protease zymogram only showed one zymogen (0.65 rf), which appear at 6 dah. Lipase was high at the time of hatching and increased until 15 dah, after which decreased gradually. Amylase was high from the beginning and until 15 dah and then decreased rapidly to almost nothing onward. Alkaline and acid phosphatases presented a high activity at the egg stage, fell slightly during the first feeding and increased again from 20 to 30 dah. Results obtained in this study show that larvae can be fed artificial diets starting on day 10 after hatching.

The teleost brain is an energetically costly organ, which raises the question of how brain anatomy is shaped by divergent ecological factors in contrasting (extreme/resource‐limited vs. benign) environments. A previous study compared different ecotypes of the teleost Poecilia mexicana in the Tacotalpa drainage system and found that cave fish had a smaller eye diameter, a smaller optic tectum and larger telencephalic lobes relative to ancestral surface‐dwelling fish. Smaller eyes and a smaller optic tectum but larger telencephalic lobes were also found in fish from a sulphidic surface habitat near one of the caves, which the authors hypothesized to result from limited vision in turbid sulphide waters. In this study, we tested if repeated transitions along a replicated, natural toxicity gradient result in repeated (‘convergent’) anatomical changes of the teleost brain. We compared ecotypes in the P. mexicana species complex that have independently evolved increased tolerance to hydrogen sulphide (H2S) in three river drainages in southern Mexico, including a phylogenetically old H2S‐adapted form (P. sulphuraria) and two P. mexicana ecotypes that represent earlier stages of adaptation to H2S. All H2S‐adapted ecotypes exhibited smaller eyes, a smaller optic tectum volume and a smaller brain volume, but larger corpora cerebelli and hypothalamic volume than fish from non‐sulphidic habitats. Drainage‐specific effects were found for the telencephalic lobes, the total brain and eye size, as sexes responded differently to the presence of H2S depending on the drainage of origin. Turbidity and toxicity in sulphidic habitats may explain patterns of brain size divergence similar in direction (but not degree) to those observed in cave ecotypes. Hence, variation in brain anatomy reflects major ecological differences, and repeated ecological gradients can result in convergent differences in brain anatomy. Nonetheless, some unique patterns of brain differentiation suggest as yet unidentified differences in selection regimes between different sulphidic springs.

The lipid class and fatty acid composition of a little-known and rarely collected alga Exophyllum wentii from Bali Island, Indonesia were determined for fresh and frozen-thawed samples using thin-layer chromatography, gas-liquid chromatography, and high-performance liquid chromatography. Glycoglycerolipids, which mainly consisted of mongalactosyldiacylglycerols (MGDG) and digalactosyldiacylglycerols (DGDG), were the predominant lipid components, accounting for 67% and 56% of the total polar lipid content in the fresh and frozen-thawed samples, respectively. Phospholipids, including phosphatidylcholines (PC) and phosphatidylglycerols (PG), were detected with lesser amounts in both samples (16 -17% of the total polar lipid content). Free fatty acids (FFA), sterols and triacylglycerols (TAG) were also detected in minor quantities; however, the FFA content in the frozen-thawed sample increased to up to 20% of the total lipid content, suggesting that hydrolysis of the membrane lipids had occurred. A crude enzyme preparation from the alga showed activities for hydrolyzing the acyl groups of the phospholipids and glycoglycerolipids. Palmitic acid (16:0) and arachidonic acid (20:4n-6) were the major fatty acids in both the total lipid and in individual polar lipid classes as well as the dominant fatty acids released from the membrane lipids by enzymatic hydrolysis. The high level of 20:4n-6 (29%) in the total lipid and the presence of considerable amounts of PC (11% of the total polar lipid) and PG (6.2%) support classification of E. wentii into the Division Rhodophyta.