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1. Correlated and decoupled evolution of adult and larval body size in frogs

   https://doi.org/10.1098/rspb.2020.1474  

   Phung, Tung X.; Nascimento, João C.; Novarro, Alexander J.; Wiens, John J. (August 2020, Proceedings of the Royal Society B: Biological Sciences)

   The majority of animal species have complex life cycles, in which larval stages may have very different morphologies and ecologies relative to adults. Anurans (frogs) provide a particularly striking example. However, the extent to which larval and adult morphologies (e.g. body size) are correlated among species has not been broadly tested in any major group. Recent studies have suggested that larval and adult morphology are evolutionarily decoupled in frogs, but focused within families and did not compare the evolution of body sizes. Here, we test for correlated evolution of adult and larval body size across 542 species from 42 families, including most families with a tadpole stage. We find strong phylogenetic signal in larval and adult body sizes, and find that both traits are significantly and positively related across frogs. However, this relationship varies dramatically among clades, from strongly positive to weakly negative. Furthermore, rates of evolution for both variables are largely decoupled among clades. Thus, some clades have high rates of adult body-size evolution but low rates in tadpole body size (and vice versa). Overall, we show for the first time that body sizes are generally related between adult and larval stages across a major group, even as evolutionary rates of larval and adult size are largely decoupled among species and clades. 

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2. Diversity, distribution and intrinsic extinction vulnerability of exploited marine bivalves

   https://doi.org/10.1038/s41467-023-40053-y  

   Huang, Shan; Edie, Stewart_M; Collins, Katie_S; Crouch, Nicholas_M_A; Roy, Kaustuv; Jablonski, David (August 2023, Nature Communications)

   Abstract Marine bivalves are important components of ecosystems and exploited by humans for food across the world, but the intrinsic vulnerability of exploited bivalve species to global changes is poorly known. Here, we expand the list of shallow-marine bivalves known to be exploited worldwide, with 720 exploited bivalve species added beyond the 81 in the United Nations FAO Production Database, and investigate their diversity, distribution and extinction vulnerability using a metric based on ecological traits and evolutionary history. The added species shift the richness hotspot of exploited species from the northeast Atlantic to the west Pacific, with 55% of bivalve families being exploited, concentrated mostly in two major clades but all major body plans. We find that exploited species tend to be larger in size, occur in shallower waters, and have larger geographic and thermal ranges—the last two traits are known to confer extinction-resistance in marine bivalves. However, exploited bivalve species in certain regions such as the tropical east Atlantic and the temperate northeast and southeast Pacific, are among those with high intrinsic vulnerability and are a large fraction of regional faunal diversity. Our results pinpoint regional faunas and specific taxa of likely concern for management and conservation. 

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3. CONFLICTING BODY-SIZE TRENDS ACROSS THE PLIO–PLEISTOCENE MOLLUSCAN TURNOVER EVENT IN THE WESTERN ATLANTIC DESPITE SUBSEQUENT NUTRIENT LIMITATION

   https://doi.org/10.1130/abs/2023AM-391080  

   Anderson, Brendan; Behn, Jessica R.; Betz, Amy; Petsios, Elizabeth; Allmon, Warren D.; Lieberman, Bruce; Hendricks, Jonathan (August 2023, Geological Society of America Abstracts with Programs)

   Preliminary data indicate between the latest Pliocene and recent approximately 85% of bivalves and 90% of gastropod species in Florida and the Atlantic Coastal Plain became extinct, with high levels of origination resulting in similar total species richness in the region today. We expected this event may have impacted molluscan body size as body size in mollusks is generally correlated with nutrient availability and primary productivity, which decreased following the Pliocene closure of the Central American Seaway. Previous work indicated small body size is associated with extinction survival during this event in both bivalves and gastropods. Where all extant and Pliocene members of surviving bivalve clades have been compared, these have also declined in size; comparable studies of all extant and Pliocene members of gastropod clades have not yet, however, been undertaken. We investigated 3 families of gastropods of differing ecology with both high turnover and at least one boundary-crossing lineage in order to assess the impact of the turnover event on each clade’s body size. These were the predatory Conidae, the herbivorous Tegulidae, and the suspension-feeding Turritellidae. These had approximately 65%, 75%, and 90% extinction, respectively, with modern­ diversity at 110%, 100%, and 10% of their respective Pliocene species richness in the region. Despite high levels of turnover, we found no general pattern of body-size change associated with the event either within clades or among boundary-crossing lineages. While many of the largest species of Conidae and Turritellidae did become extinct, this was balanced by the loss of smaller-bodied species, while the Tegulidae increased in size. Among ancestor-descendant pairs, 1 turritellid decreased in size while 1 remained unchanged, 4 Conidae decreased in size while 2 increased in size, and 1 tegulid increased in size. These data suggest that for gastropods there were complex interactions between ecology, extinction, origination, and body-size evolution associated with this event and that a more phylogenetically-diverse dataset is needed to determine whether generalizable patterns exist which may be used to predict responses to future environmental change. 

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4. Spatial filters of function and phylogeny determine morphological disparity with latitude.

   Collins, K.S. (August 2019, PloS one)

   The drivers of latitudinal differences in the phylogenetic and ecological composition of communities are increasingly studied and understood, but still little is known about the factors underlying morphological differences. High-resolution, three-dimensional morphological data collected using computerized micro-tomography (micro-CT) allows comprehensive comparisons of morphological diversity across latitude. Using marine bivalves as a model system, this study combines 3D shape analysis (based on a new semi-automated procedure for placing landmarks and semilandmarks on shell surfaces) with non-shape traits: centroid size, proportion of shell to soft-tissue volume, and magnitude of shell ornamentation. Analyses conducted on the morphology of 95% of all marine bivalve species from two faunas along the Atlantic coast of North America, the tropical Florida Keys and the boreal Gulf of Maine, show that morphological shifts between these two faunas, and in phylogenetic and ecological subgroups shared between them, occur as changes in total variance with a bounded minimum rather than directional shifts. The dispersion of species in shellshape morphospace is greater in the Gulf of Maine, which also shows a lower variance in ornamentation and size than the Florida Keys, but the faunas do not differ significantly in the ratio of shell to internal volume. Thus, regional differences conform to hypothesized effects of resource seasonality and predation intensity, but not to carbonate saturation or calcification costs. The overall morphological differences between the regional faunas is largely driven by the loss of ecological functional groups and family-level clades at high latitudes, rather than directional shifts in morphology within the shared groups with latitude. Latitudinal differences in morphology thus represent a complex integration of phylogenetic and ecological factors that are best captured in multivariate analyses across several hierarchical levels. 

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5. Specimen alignment with limited point-based homology: 3D morphometrics of disparate bivalve shells (Mollusca: Bivalvia)

   https://doi.org/10.7717/peerj.13617  

   Edie, Stewart M.; Collins, Katie S.; Jablonski, David (January 2022, PeerJ)

   Background Comparative morphology fundamentally relies on the orientation and alignment of specimens. In the era of geometric morphometrics, point-based homologies are commonly deployed to register specimens and their landmarks in a shared coordinate system. However, the number of point-based homologies commonly diminishes with increasing phylogenetic breadth. These situations invite alternative, often conflicting, approaches to alignment. The bivalve shell (Mollusca: Bivalvia) exemplifies a homologous structure with few universally homologous points—only one can be identified across the Class, the shell ‘beak’. Here, we develop an axis-based framework, grounded in the homology of shell features, to orient shells for landmark-based, comparative morphology. Methods Using 3D scans of species that span the disparity of shell morphology across the Class, multiple modes of scaling, translation, and rotation were applied to test for differences in shell shape. Point-based homologies were used to define body axes, which were then standardized to facilitate specimen alignment via rotation. Resulting alignments were compared using pairwise distances between specimen shapes as defined by surface semilandmarks. Results Analysis of 45 possible alignment schemes finds general conformity among the shape differences of ‘typical’ equilateral shells, but the shape differences among atypical shells can change considerably, particularly those with distinctive modes of growth. Each alignment corresponds to a hypothesis about the ecological, developmental, or evolutionary basis of morphological differences, but we suggest orientation via the hinge line for many analyses of shell shape across the Class, a formalization of the most common approach to morphometrics of shell form. This axis-based approach to aligning specimens facilitates the comparison of approximately continuous differences in shape among phylogenetically broad and morphologically disparate samples, not only within bivalves but across many other clades. 

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