Polygenic sex determination produces modular sex polymorphism in an African cichlid fish

For many vertebrates, a single genetic locus initiates a cascade of developmental sex differences in the gonad and throughout the organism, resulting in adults with two, phenotypically distinct sexes. Species with polygenic sex determination (PSD) have multiple interacting sex determination alleles segregating within a single species, allowing for more than two genotypic sexes, and scenarios where sex genotype at a given locus can be decoupled from gonadal sex. Here we investigate the effects of PSD on secondary sexual characteristics in the cichlid fish Metriaclima mbenjii, where one female (W) and one male (Y) sex determination allele interact to produce siblings with four possible sex classes: ZZXX females, ZWXX females, ZWXY females, and ZZXY males. We find that PSD in M. mbenjii produces an interplay of sex-linkage and sex-limitation resulting in modular variation in morphological and behavioral traits. Further, the evolution or introgression of a novel sex determiner creates additional axes of phenotypic variation for varied traits, including genital morphology, craniofacial morphology, gastrointestinal morphology, and home tank behaviors. In contrast to single-locus sex determination, which broadly results in sexual dimorphism, polygenic sex determination can induce higher-order sexual polymorphism. The modularity of secondary sexual characteristics produced by PSD provides novel context for understanding the evolutionary causes and consequences of maintenance, gain, or loss of sex determination alleles in populations.

Quantitative and Qualitative Behavioral Measurements to Assess Pain in Axolotls (Ambystoma mexicanum)

Effective pain relief in animals relies on the ability to discern pain and assess its severity. However, few objective measures exist to assess the presence and severity of pain in axolotls, and few resources are available regarding drugs and appropriate doses to provide pain relief in this species. This study evaluated behavioral tools for cageside pain assessment and validated a reproducible and reliable quantitative method to evaluate analgesic efficacy in axolotls. Animals were divided into control and treatment groups (n = 6 per group); treatment groups received buprenorphine through injection (50 mg/kg every 24 h for 48 h intracelomically) or butorphanol immersion (0.50 or 0.75 mg/L every 24 h for 48 h). Qualitative behavioral tests, adapted from other amphibian studies, included tapping on the home tank, directing water jets or physically touching specific anatomic points on the animal, and placing a novel object in the home tank. Quantitative methods used to produce noxious stimuli were the acetic acid test and von Frey aesthesiometers. Animals that were treated with analgesics did not demonstrate a significant difference compared with controls during behavioral assessment at 1, 6, 12, 25, 30, and 48 h after analgesia administration. The acetic acid test revealed a reproducible, concentration-dependent pain response. However, a significant difference in the AAT response was not observed between control and treated groups with the tested analgesics and doses.

Interaction of Predation and Intraspecific Aggression in Bluegill Sunfish Lepomis Macrochirus

Several parameters of predatory and aggressive behaviors were measured in bluegill sunfish (Lepomis macrochirus) as a function of the social condition of the fish. Subjects were observed as 1) isolated individuals, 2) maintained pairs with complete dominance but no prior residency, and 3) temporary pairs equivalent to a resident-intruder relationship. Aggressive interactions weer also recorded during feeding sessions and during non-feeding control periods. An almost complete inhibition of feeding occurred for intruders in the temporary pairs with little or no deficit seen for submissive fish in the maintained pairs when compared to individual controls. No predatory differences were found among the dominant fish of the three groups. Aggressive behavior showed little reliable change between types of session, although all forms of aggression were much higher in the temporary pairs than in maintained pairs. In a second experiment, performed to determine the effects of the transfer procedure independent of social interaction, fish were transferred from their home tank to either an empty tank or one containing a resident conspecific. A significant decrement in predatory behavior occurred when compared to measurements taken in the home tank only when subjects were transferred to aquaria containing resident fish. The data indicated that the behavioral suppression seen in intruding subjects was due entirely to an inability to respond to both prey and aggression with the latter taking precedence. No evidence was obtained to indicate any form of motivational interdependence between the behaviors studied.