Abstract Oceanographic changes due to carbon dioxide emissions have complex and varied impacts on marine calcifying taxa. Changes in calcification can unfold over decades or longer, requiring a longer-term understanding of biomineralization patterns than laboratory-based studies can provide. Here, we investigate the calcification history of the marine mussel Mytilus californianus to determine how this ecologically critical foundation species has responded to past and ongoing environmental changes in the southern end of its range within the California Current System (CCS) between 27.72° N and 34.47° N. Calcification metrics based on shell morphology, growth banding, and mineralogical structure in 130 museum-archived M. californianus specimens collected decadally from 1913 to 2010 revealed unexpected resilience in southern M. californianus shells after previous studies found calcification vulnerability in this species farther north. Shell growth data were paired with temperature datasets and regional pH records. Despite increasingly warmer and more variable conditions in the southern CCS, M. californianus shell features remained quantitatively unchanged in this region since 1913, although we present preliminary microstructural data that align with previous evidence of increased crystallographic disorder in this species. Based on overall consistencies in calcification metrics, M. californianus appears more resistant to environmental changes at the southern end of its range.
Abstract The distribution of organisms across Earth provides insight into the origin and maintenance of biodiversity. Abundant fossil evidence suggests taxa have undergone substantial range changes over time. However, biogeographic theory and models often tend to assume that clades originated in the regions where we observe them today. Understanding the prevalence of geographically dynamic clades across the tree of life provides a way to evaluate these assumptions, thereby refining key evolutionary hypotheses. We provide a review of such range-shifting clades using a two-pronged approach. First, literature searches uncovered examples across most major multicellular groups (comprising 129 clades with mismatches between fossil and modern ranges). Concurrently, we used the well-sampled mammalian fossil record as a case study, finding that more than half of its terrestrial families (51%) had substantial (>1000 km) geographic mismatches. Geographically dynamic lineages are both common and widespread, but despite their ubiquity, fossil–modern mismatches have only recently been integrated into phylogenetic and biogeographic methods and no comprehensive overview of their advantages and challenges exists. We therefore review the current state of the field and discuss case studies where fossil evidence reshaped prevailing biogeographic theory. Biogeographers must take advantage of these rich fossil histories to better elucidate evolutionary theory across space and time.
Abstract Convergent evolution is common and a testament to the repeatability of evolution. Still, non-convergence is also widespread, and a major question is whether idiosyncratic, lineage-specific changes are reflective of chance events inherent to evolutionary processes, or whether they are influenced by deterministic genetic or ecological factors. To address this question, we quantified the degree of convergence in gene expression across lineages of livebearing fishes (Poeciliidae) that span 40 million years of divergence and have colonized toxic, hydrogen-sulfide-rich springs. We asked whether the degree of convergence across lineage pairs was related to their phylogenetic relatedness and the ecological similarity of their habitats. Using phylogenetic comparative analyses, we showed that the degree of convergence in gene expression was variable across lineage pairs. While closely related lineages did not exhibit higher degrees of convergence than distantly related ones, we uncovered a strong relationship between degree of convergence and the ecological similarity among lineages. These results suggest that variation in environmental conditions that is often overlooked in simplified descriptions of habitat differences can play an important role in shaping adaptive evolution. Our study highlights the importance of multivariate approaches that capture the complexities of selective regimes and organismal responses when assessing the repeatability of evolution.
Abstract The main dilemma facing prey is how to reduce predation risk while acquiring resources. Phenotypic plasticity, by modulating traits for acquiring resources and for defences, is a key process driving this trade-off. While there is ample evidence that predator-induced within-generational plasticity depends on resources, the relationship between resources and predator-induced transgenerational plasticity (TGP) remains understudied. This study investigated how predator exposure and resource availability influence within-generational plasticity and TGP. We based our predictions on theories related to information- and state-based plasticity, two kinds of plasticity occurring in response to environmental information or alteration affecting somatic state, respectively. We conducted a two-generation laboratory experiment in the freshwater snail Physa acuta, manipulating predator cues and resource availability. Our results revealed that both types of plasticity participate in shaping the within- and transgenerational responses. Within a generation, the limited resource decreased the somatic state but did not constrain the defences. Across generations, the poor parental state decreased the offspring state even in high-resource conditions, which in turn decreased the absolute levels of their defences but increased their investment in reproduction. These results highlight the importance of integrating informational and state-based effects across generations to provide a more complete understanding of prey responses to predators.
Abstract Freshwater salinization and nutrient enrichment are intensifying globally. Despite their widespread co-occurrence, the generality of their combined effects across regions remains unclear, limiting identification of appropriate policy scales. Using outdoor freshwater ponds established >10 years ago, replicated across inland, coastal and mountain regions, we examined independent and interactive effects of elevated salinity (0, +5 and +15 g NaCl l⁻¹) and nutrient enrichment (10 : 1 N : P additions) on benthic biofilms. Salinity was the dominant driver of community structure and function. Nutrient enrichment increased green algae abundances after 30 days but did not affect biofilm function or bacterial structure. Across all regions, bacterial richness and Shannon's diversity index declined consistently with increasing salinity after 30 days and bacterial community structures differed among all salinity levels by 60 days. Responses of phototrophic groups and biofilm functions, however, were region-specific. In the inland region, high salinity increased biofilm biomass, gross primary productivity (GPP), net primary productivity (NPP) and abundances of diatoms and cyanobacteria; in the coastal region, GPP and NPP declined under high salinity with no change to phototroph abundances; while neither was affected in the mountain region. In sum, taxonomic changes in biofilm bacterial communities under salinization were consistent across regions, while functional changes varied.
