Biotic and abiotic forces govern the evolution of trophic niches, which profoundly impact ecological and evolutionary processes and aspects of species biology. Herbivory is a particularly interesting trophic niche because there are theorized trade-offs associated with diets comprised of low quality food that might prevent the evolution of herbivory in certain environments. Herbivory has also been identified as a potential evolutionary “dead-end” that hinders subsequent trophic diversification. For this study we investigated trophic niche evolution in Clupeoidei (anchovies, sardines, herrings, and their relatives) and tested the hypotheses that herbivory is negatively correlated with salinity and latitude using a novel, time-calibrated molecular phylogeny, trophic guilds delimited using diet data and cluster analysis, and standard and phylogenetically-informed statistical methods. We identified eight clupeoid trophic guilds: molluscivore, terrestrial invertivore, phytoplanktivore, macroalgivore, detritivore, piscivore, crustacivore, and zooplanktivore. Standard statistical methods found a significant negative correlation between latitude and the proportion of herbivorous clupeoids (herbivorous clupeoid species/total clupeoid species), but no significant difference in the proportion of herbivorous clupeoids between freshwater and marine environments. Phylogenetic least squares regression did not identify significant negative correlations between latitude and herbivory or salinity and herbivory. In clupeoids there were five evolutionary transitions from non-herbivore to herbivore guilds and no transitions from herbivore to non-herbivore guilds. There were no transitions to zooplanktivore, the most common guild, but it gave rise to all trophic guilds, except algivore, at least once. Transitions to herbivory comprised a significantly greater proportion of diet transitions in tropical and subtropical (<35°) relative to temperate areas (>35°). Our findings suggest cold temperatures may constrain the evolution of herbivory and that herbivory might act as an evolutionary “dead-end” that hinders subsequent trophic diversification, while zooplanktivory acts as an evolutionary “cradle” that facilitates trophic diversification.
Bibliographical noteFunding Information:
We thank the 2013 Summer Institute in Taiwan staff, P. Hundt and S. Lavoué for helpful discussions, and our friends who assisted with fieldwork at National Chiayi University and Gao Zheng Aquaculture, Taiwan, James Cook University, Australia, Rajamangala Institute of Technology, Thailand, and University of Southern Alabama, USA. We thank the following people and institutions for tissue samples: Dr. Melanie Stiassny and Dr. Barbara Brown (American Museum of Natural History), Victoria Magath (University of Hamburg Zoological Museum), Dr. Kwang-Tsao Shao (Academia Sinica Biodiversity Research Museum), Dr. Larry Page (Florida Museum of Natural History), and Mark Adams (South Australian Museum). This work was funded in part by the Lerner-Gray Memorial Fund for Marine Research (American Museum of Natural History), Dayton Research Fund (Bell Museum of Natural History, University of Minnesota), the Minnesota Agricultural Experiment Station, and the East Asia and Pacific Summer Institutes Program from the National Science Council of Taiwan and the National Science Foundation, U.S.A. ( 1316912 ). During the preparation of this manuscript J.P.E. received financial support from a National Science Foundation Graduate Research Fellowship ( 00039202 ). Appendix A
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- Diet transition
- Latitudinal gradient
- Trophic niche