The impact of paleoclimatic changes on body size evolution in marine fishes

Abstract

Body size is an important species trait, correlating with life span, fecundity, and other ecological factors. Over Earth’s geological history, climate shifts have occurred, potentially shaping body size evolution in many clades. General rules attempting to summarize body size evolution include Bergmann’s rule, which states that species reach larger sizes in cooler environments and smaller sizes in warmer environments, and Cope’s rule, which poses that lineages tend to increase in size over evolutionary time. Tetraodontiform fishes (including pufferfishes, boxfishes, and ocean sunfishes) provide an extraordinary clade to test these rules in ectotherms owing to their exemplary fossil record and the great disparity in body size observed among extant and fossil species. We examined Bergmann’s and Cope’s rules in this group by combining phylogenomic data (1,103 exon loci from 185 extant species) with 210 anatomical characters coded from both fossil and extant species. We aggregated data layers on paleoclimate and body size from the species examined, and inferred a set of time-calibrated phylogenies using tip-dating approaches for downstream comparative analyses of body size evolution by implementing models that incorporate paleoclimatic information. We found strong support for a temperature-driven model in which increasing body size over time is correlated with decreasing oceanic temperatures. On average, extant tetraodontiforms are two to three times larger than their fossil counterparts, which otherwise evolved during periods of warmer ocean temperatures. These results provide strong support for both Bergmann’s and Cope’s rules, trends that are less studied in marine fishes compared to terrestrial vertebrates and marine invertebrates.

Adaptive immune response selects for postponed maturation and increased body size

“…Because time spent growing is one of the primary determinants of body size (Dmitriew, 2011), the very presence of MHC‐based adaptive immunity could drive the evolution of body size. Such a mechanism could be one of the drivers of the macroevolutionary trend of an increase in body size over evolutionary timescales (Cope's rule), which is particularly well supported by data from marine vertebrates (Heim et al, 2015; Smith et al, 2016; Troyer et al, 2022).…”

Out of the tropics: Macroevolutionary size trends in an old insect order are shaped by temperature and predators

“…In light of this, it is somewhat surprising that intra‐ and interspecific size gradients were largely congruent in a study of various Drosophila species, with larger species found at higher latitudes (Rohner et al, 2018). This shows that in at least some taxa, there is some congruence between intra‐ and interspecific latitudinal size gradients, perhaps reflecting a common and shared body size response to lower temperatures at higher latitudes (Rohner et al, 2018; Troyer et al, 2022).…”

Quaternary megafauna extinctions altered body size distribution in tortoises

“…In summary, mean body size of tortoises has not exhibited marked fluctuations over 23 Ma, but large and rapid changes have resulted in a smaller mean body size and shifted body size distribution patterns in extant tortoises relative to their fossil counterparts. Phylogenetic analysis has provided refined insights into body size evolution across vertebrates [55][56][57][58][59][60]. However, we excluded phylogenetic comparative methods from our approach for two reasons.…”