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Researchers often use surrogate species for assessing biodiversity—organisms that can indicate the presence of additional taxa or provide insight into environmental processes. As indicators of anthropogenic impact, "cross‐taxon" surrogates are theorized to be effective shortcuts for determining how communities respond to environmental change. However, few studies have implemented cross‐taxon surrogates given the challenge of validating the strength of the relationship between surrogates and their target taxa. Trophically transmitted parasites require multiple invertebrate and vertebrate taxa to complete their life cycles (e.g., annelids, mollusks, fishes, shorebirds), making them ideal cross‐taxon surrogates of community diversity. By sampling for these parasite surrogates, it is theoretically possible to infer the composition of the overall host community based on the species of parasites present. In our study, we tested the use of parasites as cross‐taxon surrogates of biodiversity by sampling for digenetic trematodes in the mudsnail Ilyanassa obsoleta, collected from coastal shoreline environments with or without artificial structures (e.g., bulkheads, seawalls). We found that trematode richness, evenness, and diversity were all greater in snails sampled from natural shorelines versus those with artificial structures. While parasite communities clustered by shoreline type (with vs. without artificial structures), we found no differences in multivariate dispersion, or beta‐diversity, between groups in our system. At the species level, trematodes requiring polychaetes and estuarine fishes as downstream hosts dominated parasite communities at shorelines with artificial structures. These taxa are ubiquitous but more abundant in degraded environments. In contrast, trematode species requiring mollusks and shorebirds as hosts was only documented from shorelines without artificial structures (i.e., natural), which may indicate that these areas are less degraded and have greater overall host diversity. High parasite diversity in easily collected hosts (e.g., mudsnails) provides evidence that the secondary (polychaetes, crustaceans) and tertiary (fishes, shorebirds) hosts required by the parasites are present in the system. Our study also helps validate the concept of surrogate species by demonstrating how a single species can represent broader taxonomic groups. [ABSTRACT FROM AUTHOR]

Stomach morphology can provide insights into an organism's diet. Gut size or length is typically inversely related to diet quality in most taxa, and has been used to assess diet quality in a variety of systems. However, it requires animal sacrifice and time‐consuming dissections. Measures of external morphology associated with diet may be a simpler, more cost‐effective solution. At the species level, external measures of the progastric region of the carapace in brachyuran crabs can predict stomach size and diet quality, with some suggestion that this approach may also work to examine individual diet preferences and specialization at the individual level; if so, the size of the progastric region could be used to predict trends in diet quality and consumption for individuals, which would streamline diet studies in crabs. Here, we tested whether external progastric region size predicts internal stomach size across latitude and time of year for individuals of the invasive Asian shore crab Hemigrapsus sanguineus. We found that the width of the progastric region increased at a faster rate with body size than stomach width. In addition, the width of the progastric region followed different trends across sites and over time compared to stomach width. Our results therefore suggest that the progastric region may not be used as a proxy for stomach size variation across individuals. [ABSTRACT FROM AUTHOR]

Marine species are expanding polewards with rising temperatures. In the Northwest Atlantic, tropical/subtropical species native to the Caribbean have been documented as spreading into temperate regions. One such species, the green porcelain crab (Petrolisthes armatus), has been migrating up the southeastern United States coastline from Florida since the 1990s. Until 2018, the species had not been detected north of Wilmington, North Carolina (NC). Here, we document the establishment of P. armatus populations along the NC central coast. During biodiversity monitoring, we detected the first record of P. armatus in 2018 in Beaufort, NC, and subsequent records of the crab were detected at multiple locations in the region over a four-year time period (2018-2022), often at relatively high abundances. Morphological and genetic evidence confirmed the identity of P. armatus in this region and distinguished it from its less abundant native congener, P. galathinus (banded porcelain crab). While cold winter temperatures have likely limited the species' ability to spread northwards in the past, rising winter temperatures in recent years may facilitate its continued expansion. It is vital that we continue monitoring the species' population demographics in its expanding range, as well as determine community-level impacts in the region. [ABSTRACT FROM AUTHOR]

Growing evidence suggests that microbiomes have been shaping the evolutionary pathways of macroorganisms for millennia and that these tiny symbionts can influence, and possibly even control, species interactions like host–parasite relationships. Yet, while studies have investigated host–parasites and microbiomes separately, little has been done to understand all three groups synergistically. Here, we collected infected and uninfected Eurypanopeus depressus crab hosts from a coastal North Carolina oyster reef three times over 4 months. Infected crabs demonstrated an external stage of the rhizocephalan parasite, Loxothylacus panopaei. Community analyses revealed that microbial richness and diversity were significantly different among tissue types (uninfected crab, infected crab, parasite externae and parasite larvae) and over time (summer and fall). Specifically, the microbial communities from parasite externae and larvae had similar microbiomes that were consistent through time. Infected crabs demonstrated microbial communities spanning those of their host and parasite, while uninfected crabs showed more distinctive communities with greater variability over time. Microbial communities were also found to be indicators of early‐stage infections. Resolving the microbial community composition of a host and its parasite is an important step in understanding the microbiome's role in the host–parasite relationship and determining how this tripartite relationship impacts coevolutionary processes. [ABSTRACT FROM AUTHOR]

Renicolid digeneans parasitize aquatic birds. Their intramolluscan stages develop in marine and brackish-water gastropods, while metacercariae develop in molluscs and fishes. The systematics of renicolids is poorly developed, their life cycles are mostly unknown, and the statuses of many species require revision. Here, we establish based on integrated morphological and molecular data that adult renicolids from gulls Larus argentatus and Larus schistisagus and sporocysts and cercariae of Cercaria parvicaudata from marine snails Littorina spp. are life-cycle stages of the same species. We name it Renicola parvicaudatus and synonymized with it Renicola roscovitus. An analysis of the cox1 gene of R. parvicaudatus from Europe, North America and North Asia demonstrates a low genetic divergence, suggesting that this species has formed quite recently (perhaps during last glacial maximum) and that interregional gene flow is high. In Littorina saxatilis and L. obtusata from the Barents Sea, molecular analysis has revealed intramolluscan stages of Cercaria littorinae saxatilis VIII, a cryptic species relative to R. parvicaudatus. In the molecular trees, Renicola keimahuri from L. schistisagus belongs to another clade than R. parvicaudatus. We show that the species of this clade have cercariae of Rhodometopa group and outline morphological and behavioural transformations leading from xiphidiocercariae to these larvae. Molecular analysis has revealed 3 main phylogenetic branches of renicolids, differing in structure of adults, type of cercariae and host range. Our results elucidate the patterns of host colonization and geographical expansion of renicolids and pave the way to the solution of some long-standing problems of their classification. [ABSTRACT FROM AUTHOR]

Non-indigenous species may drive declines in global freshwater biodiversity. Japanese mystery snails, Heterogen japonica (previously Cipangopaludina / Bellamya / Viviparus japonica), have invaded numerous freshwater systems in North America. To resolve questions about its population demography and genetics, we surveyed ponds and rivers from six Mid-Atlantic USA locations (Richmond, Virginia to Washington, D.C.) in 2018 and 2019 for mystery snails and co-occurring indigenous snails. A random subset of each snail species (max N = 80) per location was assessed for population demographics (size, sex), and brooding embryos were counted in mystery snails. Because morphological identification can be difficult to discern from its congener, the Chinese mystery snail (Cipangopaludina chinensis), we used a mitochondrial barcoding gene (COI) to confirm identity of H. japonica and also serve as a population genetics marker. Our barcoding confirmed that the mystery snails detected in our surveys were H. japonica, and that, compared to the indigenous range, its populations have low genetic diversity and limited genetic structure. Even so, H. japonica had the highest overall catch-per-unit-effort among all snails and sites. In demographic analyses, H. japonica populations skewed towards females, and females brooding live young were the largest across all sites. The number of live young ranged from 14 to 101/female (average: 52 live young/female). Further, a linear relationship existed between brooding female shell length and the number of live young for all sites, except one. Possible explanations could include site-level differences in abiotic or biotic parameters, but this requires further research. Altogether, the snail's reproductive capacity documented here suggests that H. japonica has the potential to undergo additional population growth, especially if large females spread to new locations. Moreover, it highlights another example of an invasive species with high population abundance, demographic performance, and distributional range even with depauperate genetic diversity. [ABSTRACT FROM AUTHOR]

Trophically-transmitted endoparasites can manipulate the behavior of intermediate hosts to increase transmission to definitive hosts. Less clear, however, is whether these relationships exist when parasites and hosts have limited coevolutionary history, e.g., a native parasite infecting an invasive host. We investigated infection by the northeastern North American trematode Microphallus similis in non-native green crabs (Carcinus maenas) to assess whether infection by M. similis influenced feeding behaviors in C. maenas and if this changed with time post-infection. We manipulated infection by randomly assigning crabs to parasite exposure and control groups. We then measured individual crab behavior at five time points (pre-infection, 72 h, 1 week, 2 week, and 3 week post-infection) with an established ethogram that recorded multiple behavioral types. We also conducted righting response trials at each time point and additionally at 4 and 5 weeks post-exposure. Compared to controls, infected crabs showed little difference in recorded behaviors, and burden of infection (i.e., number of trematode cysts) was not correlated to any behavioral metric. This lack of behavioral impact occurred at all stages of infection. Active parasite penetration/establishment early in the infection process did not provoke greater behavioral response than later stages, when the encysted parasite becomes relatively dormant. Although M. similis is capable of infecting non-native C. maenas, our results suggest that it does not manipulate host behavior, possibly because of limited coevolutionary history with C. maenas in the region, or because host manipulation is unnecessary for successful completion of its life cycle. In nature, this may have implications for the crab's invasion success in the western Atlantic, where it has escaped much of its native parasite diversity. [ABSTRACT FROM AUTHOR]