Journal
BMC EVOLUTIONARY BIOLOGY
Volume 20, Issue 1, Pages -Publisher
BMC
DOI: 10.1186/s12862-020-01648-x
Keywords
Cichlid; Morphometrics; Modularity; Integration; Morphological evolution
Categories
Funding
- National Institutes of Health [R01DE026446]
- National Science Foundation [9905127]
- Direct For Biological Sciences
- Division Of Environmental Biology [9905127] Funding Source: National Science Foundation
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Background Adaptive radiations are characterized by extreme and/or iterative phenotypic divergence; however, such variation does not accumulate evenly across an organism. Instead, it is often partitioned into sub-units, or modules, which can differentially respond to selection. While it is recognized that changing the pattern of modularity or the strength of covariation (integration) can influence the range or rate of morphological evolution, the relationship between shape variation and covariation remains unclear. For example, it is possible that rapid phenotypic change requires concomitant changes to the underlying covariance structure. Alternatively, repeated shifts between phenotypic states may be facilitated by a conserved covariance structure. Distinguishing between these scenarios will contribute to a better understanding of the factors that shape biodiversity. Here, we explore these questions using a diverse Lake Malawi cichlid species complex,Tropheops,that appears to partition habitat by depth. Results We construct a phylogeny ofTropheopspopulations and use 3D geometric morphometrics to assess the shape of four bones involved in feeding (mandible, pharyngeal jaw, maxilla, pre-maxilla) in populations that inhabit deep versus shallow habitats. We next test numerous modularity hypotheses to understand whether fish at different depths are characterized by conserved or divergent patterns of modularity. We further examine rates of morphological evolution and disparity between habitats and among modules. Finally, we raise a singleTropheopsspecies in environments mimicking deep or shallow habitats to discover whether plasticity can replicate the pattern of morphology, disparity, or modularity observed in natural populations. Conclusions Our data support the hypothesis that conserved patterns of modularity permit the evolution of divergent morphologies and may facilitate the repeated transitions between habitats. In addition, we find the lab-reared populations replicate many trends in the natural populations, which suggests that plasticity may be an important force in initiating depth transitions, priming the feeding apparatus for evolutionary change.
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