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Global climatic fluctuation has significantly impacted biodiversity by shaping adaptations across numerous species. Pleistocene climate changes notably affected species’ geographic distributions and population sizes, especially fostering post-glacial expansions in temperate regions. Evolutionary theory suggests spatial sorting of morphological traits associated with dispersal in recently expanded species. However, evidence of predicted intraspecific trait variation is scant. We investigated intraspecific trait variation in five lizard species along a forest-savanna gradient affected by Pleistocene climate. Lizards serve as an ideal group to test these ideas due to climate’s known influence on their morphological traits linked to essential functions like feeding and locomotion. We assessed two hypotheses: (i) niche variation and (ii) spatial sorting. For the niche variation hypothesis, we predicted increased intraspecific variability in head dimensions with distance from stable areas. For spatial sorting, we anticipated larger hind limb sizes with increased distance from stable areas. We gathered data on five quantitative traits from 663 samples across species. There was no evidence supporting either hypothesis across the five species. Limited sample sizes, challenges in habitat modeling, or other factors might explain this lack of support. Nonetheless, our study illuminates complexities in exploring trait variation within species. The data collected here, although inconclusive, represent a crucial test for evolutionary theory.
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Geographic and temporal morphological stasis in the latest Cretaceous ammonoid Discoscaphites iris from the U.S. Gulf and Atlantic Coastal Plains
Abstract We examine temporal and spatial variation in morphology of the ammonoid cephalopod Discoscaphites iris using a large dataset from multiple localities in the Late Cretaceous (Maastrichtian) of the U.S. Gulf and Atlantic Coastal Plains, spanning a distance of 2000 km along the paleoshoreline. Our results suggest that the fossil record of D. iris is consistent with no within-species net accumulation of phyletic evolutionary change across morphological traits or the lifetime of this species. Correlations between some traits and paleoenvironmental conditions as well as changes in the coefficient of variation may support limited population-scale ecophenotypic plasticity; however, where stratigraphic data are available, no directional changes in morphology occur before the Cretaceous/Paleogene (K/Pg) boundary. This is consistent with models of “dynamic” evolutionary stasis. Combined with knowledge of life-history traits and paleoecology of scaphitid ammonoids, specifically a short planktonic phase after hatching followed by transition to a nektobenthic adult stage, these data suggest that scaphitids had significant potential for rapid morphological change in conjunction with limited dispersal capacity. It is therefore likely that evolutionary mode in the Scaphitidae (and potentially across the broader ammonoid clade) follows a model of cladogenesis wherein a dynamic morphological stasis is periodically interrupted by more substantial evolutionary change at speciation events. Finally, the lack of temporal changes in our data suggest that global environmental changes had a limited effect on the morphology of ammonoid faunas during the latest Cretaceous.
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- Award ID(s):
- 1924807
- PAR ID:
- 10349856
- Date Published:
- Journal Name:
- Paleobiology
- ISSN:
- 0094-8373
- Page Range / eLocation ID:
- 1 to 23
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1017/pab.2022.15
