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Trace element (Fe, Mn, Cr, Cu, Ni, Co, Pb, Zn, Cd, As, Hg) concentrations were assessed in marine organisms (n = 52) sampled from the Magdalena Bay lagoon complex in Baja California Sur, Mexico, a pristine marine environment. The overall trend of metal concentrations (dry weight) in the organisms was found to be Fe > Zn > Cd > Cu > Mn > Pb > As > Hg > Ni > Cr > Co. Bivalve mollusks (53.83 mg kg−1) contained twofold higher levels of metals than the finfishes (20.77 mg kg−1). Calculated BioConcentration Factor (BCF) values showed that dissolved Mn is readily bioavailable to the organisms, whereas Biota Sediment Accumulation Factor (BSAF) indicated high values for Zn, Cu and Cd. Cd and As levels were observed to be increasing with the trophic levels. Toxic elements, namely Pb, Cd and As in the studied fish species were found to be higher than the values recommended for human seafood consumption. The study provides a comprehensive baseline report on trace element bioaccumulation in several marine organisms that will aid in developing effective conservation strategies of the highly biodiverse lagoon complex.

La evolucion craneal de los mamiferos ha estado caracterizada por la modificacion de sus estructuras anatomicas, para el desarrollo de complejas estructuras; sin embargo, a pesar de la composicion de algunos arreglos ecomorfologicos craneales y mandibulares; la historia evolutiva de este grupo muestra convergencias iterativas a lo largo del tiempo, demostrando que algunos fenomenos evolutivos surgen como respuesta a condiciones similares. Desde el punto de vista filogenetico, se ha demostrado que existe una relacion compleja entre la cercania filogenetica, la integracion y la funcion; sobre la definicion de las formas del craneo de los mamiferos a lo largo de la evolucion. La probabilidad de comprobar la influencia de la historia evolutiva en la morfologia craneal de los organismos, se incrementa cuando se analizan niveles taxonomicos bajos o cuyas secuencias de divergencia moleculares son pequenas; contrario a cuando se analizan grupos mas lejanos con divergencias mayores. La estructura craneal tambien se ve influenciada por factores externos durante la ontogenia de los individuos; como resultado de los ajustes evolutivos y ecologicos entre el fenotipo y el ambiente. El habitat ha sido una de las principales fuentes de variacion morfologica, mostrando especializaciones complejas para especies que viven o pasan partes de sus ciclos de vida en ambientes acuaticos, terrestres y aereos. La dieta por su parte tambien es otro factor que ha determinado la evolucion del tamano, forma y robustez del craneo y mandibula, al igual que la forma, el tamano y la disposicion de los dientes; proporcionando especializaciones especificas para cada tipo de dieta. Las conductas de agresion tambien han modelado el craneo de este grupo animal, dado que se usa como un mecanismo de ofensa, defensa, y para sus exhibiciones ritualisticas frente a las hembras.

How fish functional morphology shapes species co-existence and assemblage diversity patterns is a fundamental issue in ecological research. In fishes, much is known about the ecomorphological relationships of feeding morphology in coral reef fishes and in freshwater taxa inhabiting distinct environments. However, little is known about the patterns and processes shaping morphological variation in other oceanic taxa; particularly those inhabiting soft bottom habitats. In this study, we assessed patterns of feeding ecomorphology in seven demersal teleost species associated with soft bottoms of the continental shelf in the central Mexican Pacific Ocean. Feeding analyses indicated that some species groups shared similar diets. Likewise, patterns of morphological variation based on geometric morphometrics demonstrated that some taxa did not differ in body shape, while patterns of variation in other species were seen in body length and height, caudal peduncle height and the anal fin anterior insertion point. A multivariate association between diet composition data and overall body shape indicated significant ecomorphological relationships, describing a continuum between species displaying benthopelagic morphology and specializing on prey with high speed swimming ability (Engraulidae), versus species with benthic morphology and specializing on fast escape prey (crustacea). The clear ecomorphological patterns observed for these seven species at both the individual and species levels imply that environmental conditions and resource availability allow these taxa to differentially inhabit and exploit the soft bottom ecosystem. Fish diversity is principally represented by the benthic morphology, although benthopelagic morphology, also show a high degree of success in this environment.

Environmental conditions may influence mating behaviour in otariids breeding in areas with elevated temperatures and intense solar radiation. Although they have evolved morphological and physiological adaptations to prevent overheating while breeding on land, under extreme temperature conditions, they must adjust their behaviour in order to thermoregulate. The California sea lion mating system is based on male competition and displays that occur while defending their territories when females are present. We studied the agonistic behaviour of adult males at two breeding colonies in Mexico with contrasting environmental characteristics: Isla Santa Margarita (ISM) (Pacific coast) and Isla San Esteban (ISE) (Gulf of California). The goal of this study was to determine which variables influence where (i.e. on land or in the water) aggressive interactions between adult males occurred using logistic regression analysis. We analysed three scenarios: (1) both islands, (2) only ISM and (3) only ISE. The best model for the first scenario included the air temperature, density of females and type of aggression. The second scenario involved the density of females, and the third scenario included the rate of female interactions. Although the California sea lion mating strategy involves monopolizing critical resources, our results indicate that density of females and rate of female interactions have a significant impact on where male aggressive interactions occur. Our results highlight how changing environmental conditions affect the behavioural plasticity of this species' mating system. Most notably, males inhabiting high-temperature environments use the thermoregulatory strategy of defending territories adjacent to the coast while remaining immersed in the water. This strategy may result in decreased polygyny in the Gulf of California colonies relative to those on the Pacific coast.

Since elasmobranchs are frequently apex predators in marine ecosystems, information on their diet is essential for understanding trophic relationships in these systems. Trophic similarity between six batoid species (Rhinoptera steindachneri, Rhinobatos glaucostigma, Dasyatis dipterura, Urotrygon aspidura, U. nana, and U. rogersi) was examined by analyzing the stomach contents of 140 individuals. Specimens were caught by the commercial shrimp fishery in the central Mexican Pacific. In total, 88.6% of the stomachs were completely to partially full, allowing the identification of 77 types of prey. The primary dietary components were crustaceans, followed by annelids and mollusks. Values of diet breadth for the six species indicated low diversity in prey items. Diet similarity suggested two trophic guilds: R. glaucostigma, U. nana, and U. aspidura belong to the cancritrophic guild (P < 0.05) and U. rogersi and D. dipterura to the annelidcrustacean guild. Rhinoptera steindachneri showed no evident pattern of association (feeding primarily on ophiuroids). In light of these results, we argue that a distribution of alimentary resources (niche partitioning) between the six species favors their coexistence. Dado que los elasmobranquios son frecuentemente depredadores tope en los ecosistemas marinos, la informacion sobre su dieta es esencial para entender las relaciones troficas en estos sistemas. La similitud trofica entre seis especies de batoideos (Rhinoptera steindachneri, Rhinobatos glaucostigma, Dasyatis dipterura, Urotrygon aspidura, U. nana y U. rogersi) fue examinada por medio del analisis de contenidos estomacales de 140 individuos. Los especimenes fueron capturados en la pesqueria comercial de camaron en el Pacifico central mexicano. En total, el 88.6% de los estomagos analizados estaban parcial o completamente llenos, permitiendo la identificacion de 77 tipos de presa. Los principales componentes en la dieta fueron los crustaceos, seguidos por anelidos y moluscos. Los valores de amplitud de dieta en las seis especies indicaron baja diversidad en los items presa. El analisis de similitud de dietas sugirio dos grupos funcionales: R. glaucostigma, U. nana y U. aspidura pertenecen al grupo “cancritrofico” (P < 0.05) y U. rogersi y D. dipterura al grupo de anelidos y crustaceos. Para R. steindachneri no hubo un patron evidente de asociacion (se alimenta principalmente de ofiuros). Con base en estos resultados, se argumenta que la distribucion de recursos alimenticios (particion del nicho) entre las seis especies favorece su coexistencia.

Foraging and the evasion of predators are fundamental for the survival of organisms, but they impose contrasting demands that can influence performance in each behavior. Previous studies suggested that foraging organisms may experience decreased vigilance to attacks by predators; however, little is known about the effect of foraging on escape performance with respect to the kinematics and the timing of the response. This study tested the hypothesis that engaging in foraging activities affected escape performance by comparing fast-start escape responses of silver-spotted sculpins Blepsias cirrhosus under three conditions: (1) control (no foraging involved), (2) while targeting prey, and (3) immediately after capture of prey. Escape response variables (non-locomotor and locomotor) were analyzed from high-speed videos. Responsiveness was lower immediately after capturing a prey item compared with the other two treatments, and latency of performance was higher in the control treatment than in the other two. Locomotor variables such as maximum speed, maximum acceleration, and turning rates did not show statistical differences among the three groups. Our results demonstrate that foraging can negatively affect two fundamental components of the escape response: (1) responsiveness and (2) latency of escape, suggesting that engaging in foraging may decrease an individual's ability to successfully evade predators.