Biology subjects

Arnold, A. E.

Publications and source records attributed to Arnold, A. E..

4 recordsLinked to original sources

bioRxiv2026

The allometry of spiracles and gill slits: a window into the respiratory capacity of rays

Metabolic rate governs the pace of life through the allocation and expenditure of energy, yet metabolic rate data are unavailable for most species. External morphological traits, such as gill slits, have been used to infer respiratory physiology and metabolism in sharks, yet, whether that pattern is generalizable across rays is unknown. In rays (Batoidea), spiracle length seems adaptive to oxygen uptake capacity, environmental oxygen availability, and activity level. Thus, we evaluate the allometry of external respiratory morphology (spiracles and gill slits) in rays using 550 museum specimens representing 88 species. We test whether spiracle length and gill slit height grow isometrically with body size (total length or disc width) within and across species. Overall, we find spiracles and gill slits are morphologically diverse, varying widely in shape within and between families. Spiracle length and gill slit height scale isometrically and are a consistent proportion of body size, despite such high morphological variability. While that proportion is consistent through ontogeny, each species proportion differs (e.g. gill slit height ranges from 0.93% of total length in Spotted Legskate to 2.93% in Pacific Electric Ray). Of the three swimming styles, pectoral oscillating species (Mobulid and Eagle Rays) may have steeper scaling of spiracle length with gill slit height - consistent with greater respiratory capacity in species with more active lifestyles. Our findings are consistent with literature hypothesizing external respiratory morphology (spiracles and gill slits) is tightly related to metabolic rate and activity level, and demonstrate the value of natural history collections in ecological research. Importantly, the isometry of both respiratory traits means that a single measure of any individual, irrespective of size, will be representative of the species thus providing a basis for expanding our understanding of metabolic morphology, enabling future work on life history, extinction risk, and ecological function.

ecology↗

bioRxiv2026

Sharks, Rays, & MPAs: Evaluating protected area coverage in national waters across species ranges

Global conservation agreements emphasize protected area coverage targets, such as the Kunming-Montreal Global Biodiversity Frameworks 30x30 target, yet their effectiveness in safeguarding biodiversity remains uncertain. We measure the intersection between marine protected area (MPAs) coverage and the distribution of sharks and rays. Using global range maps and MPA boundaries within national Exclusive Economic Zones, we calculate the percent of species ranges within MPAs, focusing on no-take areas. We reveal significant shortfalls in species-level protection. Within national waters, no Critically Endangered species has more than 5% of its range in no-take MPAs, and 79% of threatened species have less than 1%. We also find the WDPA contains major gaps in take-status reporting, only one third of countries (34%) report take-status of any MPAs to the WDPA, further limiting estimates of meaningful protection. These results highlight the implementation gap between global coverage targets and biodiversity outcomes, reinforcing the need for species-focused protection.

ecology↗

bioRxiv2024

Evaluating the Role of Endophyte-Rich Leaves in Protecting Tropical Trees Against a Generalist Herbivore and a Pathogen

1.Plants use chemical compounds and physical barriers to defend themselves against natural enemies. For instance, tough leaves are considered to be better defended than soft leaves and we can measure this spectrum of defenses via leaf functional traits. Leaf traits such as leaf chemistry, lifespan, toughness, and leaf mass per area often are a plants first line of defense. Plants with longer lifespans that invest more in leaf tissue and higher leaf mass per area (LMA) typically feature robust constitutive defenses (e.g., leaf toughness, thickness, and dense cell walls) as well. In contrast, plants that invest more in leaf nutrients and have low LMA often invest more in induced defenses. Whether constitutive or induced, leaf traits represent an environmental filter for foliar endophytic fungi (FEF), which may play an additional role in plant defense. Our overarching assumption is that FEF alter leaf fate by interacting directly or indirectly with leaf traits, thus reshaping successive FEF colonization, development of leaf traits and response to plant enemies. To evaluate this hypothesis, we inoculated seedlings of seven tropical tree species that varied in leaf traits with natural and diverse endophyte communities. We confirmed the success of our inoculations of low FEF load (E-) and high FEF load (E+) treatment groups via culturing and culture-free amplicon sequencing. We then measured leaf removal by leaf-cutter ants and leaf necrosis due to a generalist fungal pathogen. Across the experiment, we observed greater herbivory in the E- treatment compared to the E+ treatment, but no difference in pathogen damage. However, within E- and E+ treatment groups, leaves exposed to pathogen had greater leaf damage than non-exposed leaves. Dimensionality reduction of leaf functional traits (i.e., LMA, toughness, thickness, and anthocyanin levels) revealed relationships among traits and distinct host species characteristics. All leaf functional traits had significant correlations with FEF community composition. In turn, indicator species analyses reveal functional traits and taxonomic identities of FEF associated with high- and low leaf damage by natural enemies, suggesting new insights into cryptic roles of foliar symbionts in extending and modifying plant defenses in tropical forests.

ecology↗

bioRxiv2021

Secondary metabolism drives ecological breadth in the Xylariaceae

Global, large-scale surveys of phylogenetically diverse plant and lichen hosts have revealed an extremely high richness of endophytes in the Xylariales, one of the largest clades of filamentous fungi and a significant source of novel secondary metabolites (SMs). Endophytes may produce host protective antimicrobial or insecticidal SMs, as well as compounds that facilitate symbiotic establishment through suppression or degradation of host immune response, but the ecological roles of most SMs are unknown. Here we characterized metabolic gene clusters in 96 genomes of endophytes and closely related saprotrophs and pathogens in two clades of Xylariales (Xylariaceae s.l. and Hypoxylaceae). Hundreds of genes appear horizontally transferred to xylarialean fungi from distantly related fungi and bacteria, including numerous genes in secondary metabolite gene clusters (SMGCs). Although all xylarialean genomes contain hyperabundant SMGCs, we show that increased gene duplications, horizontal gene transfers (HGTs), and SMGC content in Xylariaceae s.l. taxa are linked to greater phylogenetic host breadth, larger biogeographic distributions, and increased capacity for lignocellulose decomposition compared to Hypoxylaceae taxa. Overall, our results suggest that xylarialean endophytes capable of dual ecological modes (symbiotic and saprotrophic) experience greater selection to diversify SMGCs to both increase competitiveness within microbial communities and facilitate diverse symbiotic interactions.

genomics↗