Neotropical cichlid functional morphology and macroevolution

The remarkable diversity of Neotropical cichlids. (An image showing a circular evolutionary tree in blue, green, orange and grey, surrounded by several photographs of fish, on a black background)

Adaptive radiation is a macroevolutionary process in which rapid speciation is tied to the adaptation to ecological niches. Opinions vary wildly as to whether or not adaptive radiation represents a broadly applicable pattern, responsible for contributing to much of life’s diversity, or a rarer occurrence within specific, highly diverse groups. This process has also been largely studied within the context of geographically restricted radiations, like African Rift Lake Cichlids or Caribbean Anoles.

My doctoral work focused on testing the predictions of adaptive radiation within a continentally distributed clade, the Neotropical cichlids (Cichlinae). Found across South and Central America, and as far north as Texas, Neotropical cichlids show remarkable ecological, morphological and species diversity. While less numerous than their sister clade, the African Rift Lake Cichlids, Neotropical cichlids encompass hundreds of species, and numerous convergent ecological specializations, body shapes and adaptations to their sister clade. Neotropical cichlids therefore represent a uniquely valuable system to examine the link between diversification and ecological adaptation across broad geographic scales.

My work in Cichlinae has focused on four main goals: quantifying morphological and functional variation associated with feeding, testing whether patterns of diversification follow expectations of changing ecological opportunity, examining the constraints on functional diversification, and quantifying the relationships between form, function and ecology. To address these topics, I have used dissections, image analysis and histology to collect morphometric and biomechanical data from species across the Cichlinae tree of life. I have used phylogenetic comparative methods to examine how rates of diversification have changed through time, and what macroevolutionary factors best explain functional diversity among modern Neotropical cichlids.

Quantifying shape (top) and functional (bottom) traits in Neotropical cichlids. Modified from Arbour and Lopez-Fernandez 2011 and 2018. (An image showing line drawings and photographs of fish on a white background)

Functional diversity in Neotropical cichlids has been limited by factors such as selective and constructional constraints, as well as declining ecological opportunities in South America. However, new opportunities available to cichlids following the colonization of Central America spurred an acceleration in evolutionary rates and help to drive increased functional diversity among heroine cichlids. Cichlids therefore follow one of the major predictions of adaptive radiation – that trait diversification is linked to the availability of ecological niches.

Patterns of functional evolution in South and Central American cichlilds. Modified from Arbour and Lopez-Fernandez 2016. (An image showing an evolutionary tree, a map of the Neotropics, a graph and several photographs of fish)

My continuing work on cichlids has been investigating how specific ecological adaptations and specializations have shaped functional diversity.


Selected Publications

Arbour, J.H. & López-Fernández, H. 2018. Intrinsic constraints on the diversification of Neotropical cichlid adductor mandibulae size. The  Anatomical Record 301(2):216-226 (link)

Arbour, J.H., & López-Fernández, H. 2016. Continental cichlid radiations: functional diversity reveals the role of changing ecological opportunity in the Neotropics. Proceedings of the Royal Society B 238: 20160556. (link)

Arbour, J.H. & López-Fernández, H.  2014. Adaptive landscape and functional diversity of Neotropical cichlids: implications for the ecology and evolution of Cichlinae (Cichlidae; Cichliformes). Journal of Evolutionary Biology 27(11):2431-42. (link)

López-Fernández*, H., Arbour*, J.H., Willis, S., Watkins, C., Honeycutt, R., & Winemiller, K. 2014. Morphology and efficiency of a specialized foraging behavior, substrate sifting, in Neotropical cichlid fishes. PLoS ONE9(3): e89832 [* joint first authors] (link)