Search for: All records

ABSTRACT Natural selection shapes traits during evolution including animal coloration known to be important for concealment and communication and color has been particularly salient in the explosive radiation of cichlid fish species in the rift valley lakes of East Africa. Though selection can produce variation in color via genetic substrates during early development, plasticity in coloration can occur through endocrine, neural and transcriptional cues in response to various environmental stimuli. It is well known that some animals often change color to match their visual ecology. Adult male cichlid fish (Astatotilapia burtoni, Lake Tanganyika) can switch between blue and yellow body colors. Different colors result from the expression of pigment-bearing cells, which differ in density and function between these two color morphs. We show thatA. burtoniswitches from yellow to blue depending on their visual environment by downregulating endothelin receptor B (EdnRB) mRNA via DNA hypermethylation at a single cytosine residue within its promoter. EdnRB functions in yellow chromatophores to signal the aggregation of yellow pigments, making yellow less visible. Taken together, the regulation ofEdnRBthrough DNA methylation in yellow chromatophores, in part, contributes to pigmentation changes from blue to yellow, depending on visual environment. 

Animals organize into social groups to increase collective fitness. These groups use behavior and morphological traits like color to communicate social status. Male bluegill (Lepomis macrochirus) form breeding collectives during the reproductive months. However, whether these colonies generate resource-stratified social hierarchies to manage intrasexual competition is unknown. We hypothesize that territorial position within the colony results in different body colors and behavioral profiles. To test this hypothesis, we quantified color patterns in wild communities of bluegill using computer vision, scored the behavior of lek occupying parental males, and categorically classified lek position as a function of neighboring males. From these data, we show that body coloration and behavior vary with lek position, suggesting a division of labor in the construction and maintenance of grouped territories where courtship and sexual selection take place. Collectively, these data underline the importance of male-specific morphological plasticity and its impacts on social organization. 

Within social hierarchies, rank can be dynamic and modulated by changes in molecular and/or physiological substrates. Here, we sought to better understand how social environment and rank shape male spawning behaviors and outcomes in African cichlid fish Astatotilapia burtoni. First, using a social dyad paradigm, we generated territorial (T)/Non-territorial (NT) male pairs. After establishing a stable social hierarchy, the behaviors of the Ts and NTs were recorded and scored. Afterward, pairs were separated and individually moved into a spawning phase, which consisted of a new tank with novel females and no other males where their behaviors were scored. While previous studies have shown how territorial and non-territorial males have unique behavioral profiles, we sought to deepen this interpretation with a focus on the latency of decision making, and on transition matrices representing enriched sequences of behavior. We found that while the courtship behaviors are shared between stably territorial and ascending males in the spawning phase, only the animals that were territorial in the dyad phase were the ones that were reproductively successful in the subsequent 16 h spawning phase. 

Animal colouration is fundamentally important for social communication within conspecifics to advertising threat to competitors or fitness to possible mates. Social status and animal colouration are covarying traits that are plastic in response to dynamic environments. In the African cichlid,Astatotilapia burtoni, body colouration and behaviour have been extensively reported to vary with social rank. However, the nature of the interaction between these two traits is poorly understood. We hypothesise that pigmentation patterns could be linked to the behavioural repertoires underlying social status and can be resolved to regions on the cichlid body plan. To test this hypothesis, we generated Territorial (T) and Non-territorial (NT) males and employed computer vision tools to quantify and visualise patterns/colour enrichment associated with stereotyped T/NT male behaviour. We report colour-behaviour interactions localised in specific areas of the body and face for two colour morphs illustrating a more nuanced view of social behaviour and pigmentation. Since behavioural and morphological variation are key drivers of selection in the East African Great Rift Lakes, we surmise our data may be translatable to other cichlid lineages and underline the importance of trait covariance in sexual selection and male competition. 

Synopsis Animal coloration has been rigorously studied and has provided morphological implications for fitness with influences over social behavior, predator–prey interactions, and sexual selection. In vertebrates, its study has developed our understanding across diverse fields ranging from behavior to molecular biology. In the search for underlying molecular mechanisms, many have taken advantage of pedigree-based and genome-wide association screens to reveal the genetic architecture responsible for pattern variation that occurs in early development. However, genetic differences do not provide a full picture of the dynamic changes in coloration that are most prevalent across vertebrates at the molecular level. Changes in coloration that occur in adulthood via phenotypic plasticity rely on various social, visual, and dietary cues independent of genetic variation. Here, I will review the contributions of pigment cell biology to animal color changes and recent studies describing their molecular underpinnings and function. In this regard, conserved epigenetic processes such as DNA methylation play a role in lending plasticity to gene regulation as it relates to chromatophore function. Lastly, I will present African cichlids as emerging models for the study of pigmentation and molecular plasticity for animal color changes. I posit that these processes, in a dialog with environmental stimuli, are important regulators of variation and the selective advantages that accompany a change in coloration for vertebrate animals.