Body Shape Evolution in Sunfishes: Divergent Paths to Accelerated Rates of Speciation in the Centrarchidae

Abstract

Vertebrate evolutionary radiations are the result of divergence along a variety of ecological and behavioural axes. In addition, the potential for clades to evolve along any one axis can be strongly influenced by the types and levels of phenotypic variation that are exposed to natural selection. Understanding the factors that promote and constrain morphological diversification is a central goal of evolutionary biology. Here we use the sunfishes (Centrarchidae), a perciform family containing three main clades (Lepomis, Micropterus, and a basal clade), to explore this question with respect to variation in body shape. We gathered morphological data from 26 of the 38 centrarchid species using geometric morphometrics and analyzed the resultant shape data over a time-calibrated phylogenetic tree. We find that centrarchids partitioned body shape early in their evolutionary history, a pattern that is largely associated with expansion into divergent foraging niches and elaboration of sexual ornamentation. The morphological disparity of each clade was tightly linked to integration: those clades with high disparity (Lepomis, basal clade) were the least integrated, while the opposite trend was observed in Micropterus. We also find evidence for an increase in speciation rate at the node leading to Lepomis and Micropterus, and a decline in speciation for the basal clade. Our data lead us to suggest different hypotheses for explaining accelerated speciation in Micropterus and Lepomis: invasion of a novel pursuitpredator niche that reduced resource competition (Micropterus), and the elaboration of opercular morphology (Lepomis), a trait that is linked to reproductive behaviour and facilitates mate recognition in communities with many sunfish species.

Reef fish functional traits evolve fastest at trophic extremes

“…Our results differ from those found by previous HCHsupporting studies, which suggested that feeding at high trophic levels might constrain morphological evolution in fishes 17,19,51 , as well as non-fish taxa 52 . One reason could be the broad phylogenetic sampling of our dataset in contrast with previous studies.…”

“…Studies focused on single species or small clades suggest that the evolution of high trophic position should constrain rates of functional trait evolution due to the constraints imposed by feeding on evasive energy-rich prey items relative to lower trophic levels [16][17][18][19] . We term this the height constraint hypothesis (HCH).…”

The evolution of jaw protrusion mechanics has been tightly coupled to bentho-pelagic divergence in damselfishes (Pomacentridae)

“…other fishes, shrimps) typically have large mouths and utilize fast ram strikes (Higham, 2007;Higham et al, 2007), but large mouths reduce suction feeding ability, which is only efficient within roughly one mouth diameter from the prey (Day et al, 2005;Wainwright et al, 2001). Although planktivorous damselfishes do have the largest standardized gapes (Table 5), their mouth sizes are nowhere near as large as those of piscivorous groupers (Serranidae), sunfishes (Centrarchidae) or cichlids (Cichlidae), and remain small enough to promote suction production (Cooper et al, 2010;Oufiero et al, 2012;Smith et al, 2015). We see no body ram specialists among the damselfishes and it has recently been suggested that the structure of their pharyngeal jaws may constrain their ability to specialize in larger prey, such as elusive fishes, whose capture is facilitated by body ram feeding strikes (McGee et al, 2015a).…”

Bluegill sunfish use high power outputs from axial muscles to generate powerful suction-feeding strikes

“…Not only do sunfish have different feeding kinematics but, compared with the fusiform bass, they also have shorter, deeper and more laterally compressed bodies and a smaller gape (Fig. 1B) (Smith et al, 2015;Werner, 1977).…”