Body Size Evolution and Diversity of Fishes using the Neotropical Cichlids (Cichlinae) as a Model System

The influence of body size on an organism’s physiology, morphology, ecology, and life history has been considered one of the most fundamental relationships in ecology and evolution. The ray-finned fishes are a highly diverse group of vertebrates. Yet, our understanding of diversification in this group is incomplete, and the role of body size in creating this diversity is largely unknown. I examined body size in Neotropical cichlids (Cichlinae) to elucidate the large- and small-scale factors affecting body size diversity and distribution, and how body size shapes species, morphological, and ecological diversity in fishes. Characterization of body size distributions across the phylogeny of Neotropical cichlids revealed considerable overlap in body size, particularly in intermediate-sized fishes, with few, species-poor lineages exhibiting extreme body size. Three potential peaks of adaptive evolution in body size were identified within Cichlinae. I found freshwater fishes globally tend to be smaller and their distributions more diverse and right-skewed than marine counterparts, irrespective of taxonomy and clade age, with a strengthening of these trends in riverine systems. Comparisons of Neotropical cichlid body size diversity and distribution to this broader context shows that body size patterns are largely abnormal compared to most freshwater fishes, particularly those of the Neotropics. This implies that small body size is rarer in Cichlinae, despite several independent cases of body size decrease in this lineage. I found that these small-bodied lineages are miniaturized cichlids, exhibiting strong reduction in body size, as well as paedomorphic characters and ontogenetic truncation compared to their sister taxa. Further examination of ontogenies across Neotropical cichlids found considerable shape conservatism over ontogeny and phylogeny, with cichlids following similar ontogenetic trajectories. Therefore, ontogenetic pathways do not contribute considerably to morphological divergence seen in adults, with divergence likely occurring in the larval stage or perhaps during embryology. The evolution of ontogeny, body size, and shape did not correspond to a unique adaptive peak in miniatures, or three body size optima predicted from the distribution of size across the phylogeny. Rather, it is complex and, like early trait divergence previously seen, diversifies early in the phylogeny across the major lineages of Neotropical cichlids.Ph.D.2020-07-11 00:00:0