Tempo Of Morphological Evolution Research Articles

Estimating morphological diversity and tempo with discrete character-taxon matrices: implementation, challenges, progress, and future directions

Discrete character-taxon matrices are increasingly being used in an attempt to understand the pattern and tempo of morphological evolution; however, methodological sophistication and bespoke software implementations have lagged behind. In the present study, an attempt is made to provide a state-of-the-art description of methodologies and introduce a new R package (Claddis) for performing foundational disparity (morphologic diversity) and rate calculations. Simulations using its core functions show that: (1) of the two most commonly used distance metrics (Generalized Euclidean Distance and Gower's Coefficient), the latter tends to carry forward more of the true signal; (2) a novel distance metric may improve signal retention further; (3) this signal retention may come at the cost of pruning incomplete taxa from the data set; and (4) the utility of bivariate plots of ordination spaces are undermined by their frequently extremely low variances. By contrast, challenges to estimating morphologic tempo are presented qualitatively, such as how trees are time-scaled and changes are counted. Both disparity and rates deserve better time series approaches that could unlock new macroevolutionary analyses. However, these challenges need not be fatal, and several potential future solutions and directions are suggested.

Trait decoupling promotes evolutionary diversification of the trophic and acoustic system of damselfishes.

Trait decoupling, wherein evolutionary release of constraints permits specialization of formerly integrated structures, represents a major conceptual framework for interpreting patterns of organismal diversity. However, few empirical tests of this hypothesis exist. A central prediction, that the tempo of morphological evolution and ecological diversification should increase following decoupling events, remains inadequately tested. In damselfishes (Pomacentridae), a ceratomandibular ligament links the hyoid bar and lower jaws, coupling two main morphofunctional units directly involved in both feeding and sound production. Here, we test the decoupling hypothesis by examining the evolutionary consequences of the loss of the ceratomandibular ligament in multiple damselfish lineages. As predicted, we find that rates of morphological evolution of trophic structures increased following the loss of the ligament. However, this increase in evolutionary rate is not associated with an increase in trophic breadth, but rather with morphofunctional specialization for the capture of zooplanktonic prey. Lineages lacking the ceratomandibular ligament also shows different acoustic signals (i.e. higher variation of pulse periods) from others, resulting in an increase of the acoustic diversity across the family. Our results support the idea that trait decoupling can increase morphological and behavioural diversity through increased specialization rather than the generation of novel ecotypes.