Biology subjects

Harper, E. M.

Publications and source records attributed to Harper, E. M..

4 recordsLinked to original sources

bioRxiv2024

Molecular phylogenetics of the superfamily Stromboidea (Caenogastropoda): new insights from increased taxon sampling

The superfamily Stromboidea is a clade of morphologically distinctive gastropods which include the iconic Strombidae, or true conchs. In this study, we present the most taxonomically extensive phylogeny of the superfamily to date, using fossil calibrations to produce a chronogram and extant geographical distributions to reconstruct ancestral ranges. From these results, we confirm the monophyly of all stromboidean families; however, six genera are not monophyletic using current generic assignments (Strombidae: Lentigo, Canarium, Dolomena, Doxander; Xenophoridae: Onustus, Xenophora). Within Strombidae, analyses resolve an Indo-West Pacific (IWP) clade sister to an East Pacific/Atlantic clade, together sister to a second, larger IWP clade. Our results also indicate two pulses of strombid diversification within the Miocene, and a Tethyan/IWP origin for Strombidae - both supported by the fossil record. However, conflicts between divergence time estimates and the fossil record warrant further exploration. Species delimitation analyses using the COI barcoding gene support several taxonomic changes. We synonymise Euprotomus aurora with Euprotomus bulla, Strombus alatus with Strombus pugilis, Dolomena abbotti with Dolomena labiosa, and Dolomena operosa with Dolomena vittata. We identified cryptic species complexes within Terebellum terebellum, Lambis lambis, "Canarium" wilsonorum, Dolomena turturella and Maculastrombus mutabilis. We reinstate Rimellopsis laurenti as a species (previously synonymised with R. laurenti) and recognise Harpago chiragra rugosus and Lambis truncata sowerbyi valid at the rank of species. Finally, we establish several new combinations, rendering Lentigo, Dolomena, and Canarium monophyletic: Lentigo thersites, Dolomena robusta, Dolomena epidromis, Dolomena turturella, Dolomena taeniata, Dolomena vanikorensis, D. vittata, "Canarium" wilsonorum, Hawaiistrombus scalariformis, Maculastrombus mutabilis, Maculastrombus microurceus.

zoology↗

bioRxiv2024

Evolution of Large Eyes in Stromboidea (Gastropoda): Impact of Photic Environment and Life History Traits

AO_SCPLOWBSTRACTC_SCPLOWEyes within the marine gastropod superfamily Stromboidea range widely in size, from 0.2 to 2.3 mm, the latter being the largest known eyes of any gastropod. However, the evolutionary pressures underlying this variation remain unknown. Here, we use the wealth of material available in museum collections to explore the impact of ecological factors that affect light availability (ocean depth, turbidity and diel activity) on the evolution of eye size and structure within Stromboidea. We construct the most taxonomically extensive phylogeny of Stromboidea to date as a framework to investigate these relationships. Our results suggest that depth is a key light-limiting factor in stromboid eye evolution; here, increasing water depth is correlated with increasing aperture width relative to lens diameter (p = 0.043), and therefore an increasing investment in sensitivity in dim light environments. In the clade containing all large-eyed families (Strombidae, Rostellariidae and Seraphsidae), cathemeral species had wider eye apertures relative to lens sizes than diurnal species (p = 0.002), thereby prioritising sensitivity over resolution. These cathemeral species also had smaller body sizes than diurnal species (p = 0.002); this may suggest that animals with smaller shells are more vulnerable to shell-crushing predators, and therefore avoid the higher predation pressure experienced by animals active during the day. Within the large-eyed stromboid clade, ancestral state reconstruction estimates that absolute eye size increased above 1 mm twice independently. Due to the high energetic investment associated with large eye sizes, this repeated increase in eye size suggests that higher performance vision is important in behavioural tasks within these families. In addition, we note that species with more robust escape responses tend to have larger eyes than those that do not: for example, strombids have 1.79 {+/-} 0.31 times the eye size that would be expected from their body size (based on Stromboidea as a whole) and are known to display either a rapid escape response from an approaching predator or withdrawal into the shell. By contrast, the small-eyed xenophorids have 0.59 {+/-} 0.30 times the expected eye size, and are only known to withdraw when threatened.

evolutionary biology↗

bioRxiv2022

Evolutionary conservation and divergence of the transcriptional regulation of bivalve shell secretion across life history stages

Adult molluscs produce shells with diverse morphologies and ornamentations, different colour patterns and microstructures. The larval shell however, is a phenotypically more conserved structure. How do developmental and evolutionary processes generate varying diversity at different life history stages? Using live-imaging, histology, scanning electron microscopy and transcriptomic profiling, we have described shell development in a heteroconchian bivalve the Antarctic clam, Laternula elliptica and compared it to adult shell secretion processes in the same species. Adult downstream shell genes, such as those encoding extracellular matrix proteins and biomineralisation enzymes, were largely not expressed during shell development, and instead, a development-specific downstream gene repertoire was expressed. Upstream regulatory genes such as transcription factors and signalling molecules were conserved between developmental and adult shell secretion. Comparing heteroconchian transcriptomic data with recently reported pteriomorphian larval shell proteome data suggests that, despite being phenotypically more conserved, the downstream effectors constituting the larval shell "tool-kit" may be as diverse as that of adults. Overall, our new data suggests that a larval shell formed using development-specific downstream effector genes is a conserved and ancestral feature of the bivalve lineage, and possibly more broadly across the molluscs.

evolutionary biology↗

bioRxiv2018

Plasticity and environmental heterogeneity predict geographic resilience patterns of foundation species to future change

Although geographic patterns of species sensitivity to global environmental changes are defined by interacting multiple stressors, little is known about the biological mechanisms shaping regional differences in organismal vulnerability. Here, we examine large-scale spatial variations in biomineralisation under heterogeneous environmental gradients of temperature, salinity and food availability across a 30{degrees} latitudinal range (3,334 km), to test whether plasticity in calcareous shell production and composition, from juveniles to large adults, mediates geographic patterns of resilience to climate change in critical foundation species, the mussels Mytilus edulis and M. trossulus. We find mussels produced thinner shells with a higher organic content in polar than temperature regions, indicating decreasing shell calcification towards high latitudes. Salinity was the major driver of regional differences in mussel shell deposition, and in shell mineral and organic composition. In low-salinity environments, the production of calcite and organic shell layers was increased, providing higher resistance against dissolution in more corrosive waters. Conversely, under higher-salinity regimes, increased aragonite deposition suggests enhanced mechanical protection from predators. Interacting strong effects of decreasing salinity and increasing food availability on the compositional shell plasticity in polar and subpolar mussels during growth predict the deposition of a thicker external organic layer (periostracum) under forecasted future environmental conditions. This marked response potential of Mytilus species suggests a capacity for increased protection of high-latitude mussel populations from ocean acidification. Our work illustrates that mechanisms driving plastic responses to the spatial structure of multiple stressors can define geographic patterns of unforeseen species resilience to global environmental change.

ecology↗