Crayfish Cambarus Research Articles

A multi-method approach for assessing the distribution of a rare, burrowing North American crayfish species.

Primary burrowing crayfishes face high extinction risk, but are challenging to study, manage, and conserve due to their difficult-to-sample habitat (i.e., terrestrial burrows) and low population densities. We apply here a variety of methods to characterize the distribution, habitat associations, and conservation status of the Boston Mountains Crayfish Cambarus causeyi (Reimer, 1966), an endemic burrowing crayfish found only in the Ozark Mountains of Arkansas, United States. We used species distribution modeling (SDM) on historic occurrence records to characterize the distribution and macro-scale habitat associations of this species. We then ground-truthed SDM predictions with conventional sampling, modeled fine-scale habitat associations with generalized linear models (GLM), and lastly developed and tested an environmental DNA (eDNA) assay for this species in comparison to conventional sampling. This represents, to our knowledge, the first successful eDNA assay for a terrestrial burrowing crayfish. Our MaxEnt-derived SDM found a strong effect of average annual precipitation on the historic distribution of C. causeyi, which occurred most frequently at locations with moderately high average annual precipitation (140-150 cm/yr) within our study region. Cambarus causeyi was difficult to detect by conventional sampling in 2019 and 2020, found at only 9 of 51 sites (17.6%) sampled by searching for and manually excavating crayfish burrows. Surprisingly, habitat suitability predicted from our MaxEnt models was not associated with contemporary C. causeyi occurrences per GLMs. Instead, C. causeyi presence was negatively associated with both sandy soils and the presence of other burrowing crayfish species. Poor SDM performance in this instance was likely caused by the omission of high resolution fine-scale habitat data (e.g., soils) and biotic interactions from MaxEnt models. Finally, our eDNA assay detected C. causeyi from six of 25 sites (24.0%) sampled in 2020, out-performing conventional surveys by burrow excavation for this species. Given the difficulty of studying primary burrowing crayfishes and their high conservation need, we propose that eDNA may become an increasingly important monitoring tool for C. causeyi and similar species.

Seasonal context of Bristly Cave Crayfish Cambarus setosus habitat use and life history

Cave crayfishes are important members of groundwater communities, but many cave crayfishes are threatened or endangered. Unfortunately, we lack basic life history and ecological data that are needed for developing conservation plans for most cave crayfishes, especially the role of seasonal and annual fluctuations in structuring populations. Therefore, we determined the seasonal life history and habitat use of Cambarus setosus in Smallin Civil War Cave, Christian County, Missouri, United States. We conducted visual crayfish surveys over a 400 m section of the cave from 2006 to 2019. We used multinomial logit, multiple linear regression, and logistic regression models to estimate crayfish substrate, water depth, and water velocity use, respectively. All models included sex, carapace length, season, distance into the cave, and interactions between all variables and sex as predictor terms. We also used t-tests to assess morphometric differences between male and female crayfish. Six mark-recapture events (2010 to 2019) were used to estimate population sizes using a nil-recapture model. We attempted to age eight individuals using gastric mill bands, but annual bands were not discernable. We found reproductively active males during all seasons. We captured one ovigerous female during the spring, though ovigerous females were observed during show cave tours during spring, summer, and autumn. Male C. setosus were more likely to use homogenous and heterogeneous rock substrates and shallower and calmer water when compared to females; however, these relationships varied based on distance into the cave and season. Females sampled were significantly larger than males, and males regenerated chelae more often. Minimum population size estimates ranged from 9 to 159 individuals and indicated the population was relatively stable. Our data provide both a baseline population estimate for comparison with future studies and valuable trait information that is often lacking but useful for developing conservation efforts.

Distribution, natural history, and conservation of Cambarus dubius in Pennsylvania

ABSTRACT Due to their burrowing lifestyles that make them difficult to sample, the distributions and habitat associations of most burrowing crayfishes are poorly understood. A distributional study was conducted in south-western Pennsylvania to better understand the range and habitat associations of the primary burrowing crayfish Cambarus dubius within the state. A total of 790 new sites and six previously surveyed sites were sampled between the Chestnut Ridge and Allegheny Mountains, with the majority of these localities being roadside ditches. Crayfish were collected using a combination of burrow excavation, baited lines, and by hand. We utilised permutation-based t-tests to determine differences in habitat variables between sites with and without C. dubius and sites with and without any burrowing crayfish species. Cambarus dubius was collected from 61 total sites, and active crayfish burrows were observed at 137 additional sites. Cambarus carinirostris was collected from 13 sites, Lacunicambarus thomai was collected from six sites, and an exuvia of Procambarus acutus was collected from a stream at one site. New behavioural observations for C. dubius juveniles were observed while collecting specimens with baited lines. Sites with C. dubius had significantly more canopy cover and deciduous forest land cover and significantly less pasture-hay land cover than sites without C. dubius. Sites with burrowing crayfishes (all species) had significantly more canopy cover and deciduous forest land cover and significantly lower elevation, depth to the water table, percent sand substrate and pasture-hay land cover than sites without burrowing crayfish. In Pennsylvania, Cambarus dubius has not expanded its range in comparison to its historical range, and populations appear to be concentrated primarily in the southern valleys of the Chestnut Ridge and Allegheny Mountains.

A new species of Pterodrilus (Branchiobdellida: Clitellata) from the upper Yadkin-Pee Dee River Basin of North Carolina

ABSTRACT A new species of branchiobdellidan, Pterodrilus leiteri n. sp., is described from the anterior cephalothorax of the crayfish Cambarus longulus from north-western North Carolina, USA. Like its 10 congener species, P. leiteri n. sp. is diminutive, with a maximum body length < 1 mm. It can be distinguished from other members of Pterodrilus by the number and position of dorsal ridges and projections. Unique to this species are three pairs of twinned dorsal unbranched digitiform projections on segments 3, 4, and 5. Our discovery adds to our understanding of diversity within an unusual and poorly understood genus, Pterodrilus, and more generally, branchiobdellidan fauna in the southeastern USA.

Life history of the Big Sandy crayfish Cambarus callainus Thoma, Loughman &amp; Fetzner, 2014 (Decapoda: Astacoidea: Cambaridae), an imperiled crayfish in the central Appalachian coalfields, USA

AbstractThe Big Sandy crayfish, Cambarus callainusThoma, Loughman &amp; Fetzner, 2014, endemic to the Big Sandy River basin in the central Appalachians, USA, was listed by the United States Fish &amp; Wildlife Service as threatened under the Endangered Species Act in 2016 due to limited and declining range. In March 2018 we began a twelve-month study of the species at the Dry Fork watershed in West Virginia, USA and the Russell Fork watershed in Virginia, USA to document annual life history, reveal if seasonal molting occurs, determine the reproductive season and fecundity, and define its life history strategy. Egg-bearing females were only captured in August; however, a single female was collected with free-living craylings in April, suggesting possible overwintering maternal care or a potential early spring oviposition event. Mating likely occurred between May and June and potentially into the fall and early winter. Five to six size-class cohorts were observed, and we speculate that C. callainus could live up to five years or more. Analysis of morphometric data suggests that females undergo form change, displaying larger chelae and wider abdomens. The smallest Form I male collected had a total carapace length (TCL) of 31.5 mm and the smallest Form I female 32.8 mm. The largest male collected was Form I with a TCL of 55.9 mm. Similar to other species of Cambarus, C. callainus appears to exhibit K-selected life history traits: Fewer and larger eggs, relatively longer maternal care, larger but slow growing, and long lived. The life history information described should prove invaluable to those engaging in conservation efforts for this threatened species.

The features of an emerging whispovirus isolate from freshwater crayfish

A highly lethal freshwater crayfish Cambarus clarkii whispovirus (WSSV-Cc) was isolated from a naturally infected host. A large number of viral particles with typical nimavirus characters were observed in host cells. Genomic architecture and genetic evolution of this extremely virulent pathogen were uncovered. WSSV-Cc has a double-stranded DNA genome containing 287,179 bp, encoding 180 putative ORFs. Congruence analysis was performed between WSSV-Cc and known nimavirus genomes. The genome of WSSV-Cc is smaller than that found in isolates sampled before 2010, but is similar in size to that of recent isolates, which provided new evidence for the shrinkage of nimavirus genome size during evolution. Phylogenetic analysis with the complete genome also showed connections between genome size and evolutionary relationship. Twenty low-similarity genes and three variable regions were identified from the WSSV-Cc genome. In addition, two recombination events were detected in the WSSV-Cc genome, and analysis of the recombinant regions showed a close relationship among the three freshwater crayfish nimaviruses. These findings provide us the morphological, genomic, and genetic characters of an emerging whispovirus, which will broaden our understanding to nimaviruses and be useful for diagnosis of crayfish viral disease.

Big Sandy Crayfish (Cambarus callainus) Habitat Affinity in Proximity to Bridges and Assessed via Radio Telemetry

Cambarus callainus (Big Sandy Crayfish) is a federally threatened species endemic to the coalfields of Kentucky, Virginia, and West Virginia. Existing datasets involving this species reflect broad/seasonal natural history trends, but conservation managers are still in need of a fine-scale, high resolution understanding of daily microhabitat utilization and movement patterns. The WVDOT has identified multiple locations within C. callainus range where in-stream bridge infrastructure requires complete reconstruction in a timely manner. Construction projects occurring within waterways supporting C. callainus could represent a threat to the crayfish community, but the extent of such effects is currently unknown. To identify potential disruptions to C. callainus populations we aim to determine the extent of site fidelity, peak and minimum activity periods, and preferred microhabitat utilization assessed by radiotracking C. callainus during and after active construction. Collected data will be interpreted to determine further conservation and management practices necessary for protection of C. callainus. Findings will allow organizations such as the WVDOT to move forward with necessary infrastructure projects while mitigating further anthropogenic impact to this vulnerable species.

Conservation Assessment of Cambarus dubius in Pennsylvania with Distribution Notes on Lacunicambarus thomai.

Burrowing crayfishes are poorly understood animals that face conservation and management issues due to a lack of distribution and ecological data. Within Pennsylvania, the burrowing crayfish Cambarus dubius has a limited distribution and its conservation status within the state is unranked. An assessment was conducted in southwestern Pennsylvania to assess the conservation status of C. dubius throughout its historic range. GIS-landscape data was used to analyze potential predictors of presence/absence. Six historic sites and 790 new sites were sampled for the presence of C. dubius. Of the 796 sites sampled, C. dubius was collected from 61 sites. Active crayfish burrows were present at 137 additional sites; these are predicted to be those of C. dubius due to the structure of the burrows. Additional biological and ecological data on C. dubius are also provided. The global model produced from logistic regression analysis was unable to predict variables of presence/absence; suggestions for additional variables to better predict presence/absence of C. dubius are provided. Collections also yielded populations of Lacunicambarus thomai within the range of C. dubius and are the easternmost within Pennsylvania.

Extensive regional endemism and cryptic diversity in the Tennessee and Kentucky, USA populations of the burrowing crayfish Cambarus deweesae (Bouchard &amp; Etnier, 1979) (Decapoda: Astacidea: Cambaridae) as revealed by molecular genetics

Abstract The southeastern United States is a global hotspot for crayfish biodiversity, with more than 300 described species in the region. Some of this diversity is unfortunately being threatened by anthropogenic activities and nearly one fifth of the North American crayfish species are currently threatened with extinction. Efforts to protect crayfish species have been hindered by a lack of information regarding their taxonomy, distribution, and conservation status. Here we target populations of the burrowing valley flame crayfish, Cambarus deweesae (Bouchard &amp; Etnier 1979) for molecular taxonomy investigation. This species was originally known from the Clinch and Emory subdrainages in eastern Tennessee but it is currently listed as state endangered. The reporting of additional populations in Tennessee and Kentucky, however, has led to uncertainty about its conservation status. We analyzed sequence data from three mitochondrial genes (COI, 12S rRNA, and 16S rRNA) and from one nuclear gene (GAPDH) to decipher taxonomic questions regarding 15 crayfish populations, including 13 populations that are morphologically similar to C. deweesae (type locality sensu stricto). Combined analysis of all four genes demonstrated reciprocal monophyly for 14 out of 15 populations surveyed. Species delimitation methods, including GMYC and ABGD, identified between 11 and 13 new distinct genetic entities based on sequence divergence at the mitochondrial COI gene. Molecular results are combined with information on morphology and distribution in order to resolve taxonomic uncertainties within C. deweesae and its close relatives. The study highlights the need for fine-scale investigations into the phylogeography of North American burrowing crayfishes.

Identifying Habitat Utilization and Movement of a Federally Endangered Narrow Endemic Crayfish Species, Cambarus veteranus (Guyandotte River crayfish) via Radio Telemetry

The movement and habitat selection of the federally endangered crayfish Cambarus veteranus (Guyandotte River Crayfish) was investigated via radio telemetry. The project was initiated to determine the feasibility and success of tracking a federally endangered Appalachian crayfish. Tracking occurred in the Clear Fork drainage of the Guyandotte River, Wyoming County, West Virginia, during the summer of 2018. Transmitters weighing 1.2 g were affixed to the ventral side of the right chela of five C. veteranus individuals and were released at their point of capture. Individuals were tracked three times daily for three consecutive days followed by a 6 day non-interaction period. Following the non-interaction period, animals were then tracked once daily every 2 – 3 days for approximately 4 weeks. When an individual was located, the total distance traveled and the micro/macrohabitat type was noted. Water depth, water temperature, current velocity, and distance to the nearest bank were also measured at each individual’s position. Our preliminary results provided interesting insight about the ecology and movement of C. veteranus and showed far greater movement for C. veteranus than expected, with a single crayfish moving over 480 m. Differences in movement behavior was observed between tracked males and females with males moving more frequently and traveling further than females. Although nighttime tracking was not completed, it was assumed that the majority of movement occurred during the night. Of the five crayfish tracked, four were retrieved at the completion of the study. No crayfish appeared to be harmed or impeded by the transmitters.

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Abstract In crayfish, intraspecific coloration can vary due to a variety of factors such as diet, genetic variation, environment, and ontogeny. Ortmann (1906) hypothesized that the crayfish Cambarus bartonii bartonii and Faxonius obscurus exhibit an ontogenetic shift in color change, with greener coloration in younger individuals of both species diminishing with age in larger specimens. However, this hypothesis has never been quantitatively tested. This work incorporated digital image analysis to quantify coloration of samples of C. b. bartonii and F. obscurus collected from two locations, respectively, in an eastern Pennsylvania stream. Examination for relationships between coloration (percent “green dominance”, i.e., the proportion of green in comparison to blue and red in photographs) and body size did not reveal any significant relationship between these variables in either crayfish species. Therefore, this study does not support the presence of ontogenetic color change in C. b. bartonii and F. obscurus, and suggests intraspecific variation of color in both species may be primarily influenced by other factors.

The Conhaway Crayfish (Cambarus (C.) appalachiensis), a new species of crayfish (Decapoda: Cambaridae) from the New River Basin of Virginia and West Virginia, USA.

The Conhaway Crayfish is a stream-dwelling species endemic to the greater New River basins of Virginia and West Virginia. The new species is morphologically most similar to the Teays River Crayfish (Cambarus sciotensis). Conhaway Crayfish can be differentiated from Teays River Crayfish by its more elongated chelae which possess a single mesial row of tubercles, reduced to no tuberculation on the dorsal-longitudinal ridge of the dactyl, and reduced lateral impression. Teays River Crayfish have a more subrectangular chelae with two rows of mesial margin tubercles on the chelae, as well as both a pronounced dorsal-longitudinal ridge and pronounced lateral impression. Several chelae meristic ratios also differentiate Conhaway Crayfish from Teays River Crayfish. Within the New, Gauley, and lower portions of the Greenbrier basins Conhaway Crayfish are the dominant tertiary burrowing Cambarus species, and as such, the species is considered stable across its range.

Reproductive dependence of a branchiobdellidan annelid on its crayfish host: confirmation of a mutualism

The ectosymbiotic branchiobdellidan Cambarincola ingens Hoffman, 1963 can increase the growth and reduce mortality of the crayfish Cambarus chasmodactylus James, 1966. These results suggest that these two species are engaged in a cleaning symbiosis mutualism. However, the potential benefits C. ingens derives from the association, specifically its reproductive dependence on the crayfish, have not been examined experimentally. We conducted two experiments to determine if C. ingens was reproductively dependent on C. chasmodactylus. In the experiments, worms only laid cocoons on live crayfish. Also, significantly more cocoons were laid on larger crayfish which was consistent with a survey of worm and cocoon abundance on crayfish collected from a local river. These results suggest that C. ingens is dependent on its crayfish host for reproduction. The association between C. chasmodactylus and C. ingens is a mutualism, at least under environmental conditions in which crayfish survival and growth are enhanced by the worms.

Ontogenetic shift in host tolerance controls initiation of a cleaning symbiosis

When the interests of mutualists are not perfectly aligned, control mechanisms that modulate interactions can maintain mutually beneficial outcomes and stabilize mutualisms over evolutionary time. However, the costs and benefits of symbiosis often change with ontogeny and whether control mechanisms are adjusted to reflect ontogenetic changes is largely unknown. We examined the recently described cleaning symbiosis between crayfishCambarus chaugaensisand ectosymbiotic annelids (Xironodrilus appalachius) for evidence of ontogenetic changes in symbiont control.Xironodrilus appalachiusprovide a beneficial cleaning service toC. chaugaensisby removing epibiotic accumulations from the gills, but crayfish also incur costs via density‐dependent facultative parasitism of gill tissue. A series of laboratory experiments using crayfish from three size (age) – classes demonstrated that crayfish use grooming to limit cleaner density and grooming effects on cleaners varied with crayfish age. Small crayfish quickly removed essentially all of their cleaners. Intermediate crayfish removed most of their cleaners, but some cleaners persisted at a location apparently inaccessible to grooming and far from the gill chamber. Large crayfish removed a smaller proportion of cleaners and cleaners were allowed access to the gill chamber, thus initiating the cleaning symbiosis. Cleaner removal was not dependent on cleaner density, suggesting that crayfish do not regulate cleaners to a specific density. Experimental results were corroborated by patterns observed during a field survey. We argue decreased cleaner removal and relaxed control of cleaner attachment sites corresponds to ontogenetic changes in the costs and benefits of symbiosis. This study integrates two major theoretical perspectives from ecological literature; control mechanisms and ontogenetic shifts, and illustrates how changes in control mechanisms with ontogeny may favor life‐long positive outcomes of symbiosis. Ontogenetic shifts in the costs and benefits of symbiosis may be common; therefore future theoretical and empirical studies of symbioses should incorporate both perspectives.

TAT-mediated oral subunit vaccine against white spot syndrome virus in crayfish

White spot syndrome virus is a highly pathogenic virus that infects crayfish and other crustaceans. VP28 is one of its major envelope proteins, and plays a crucial role in viral infection. Cell-penetrating peptides are short peptides that facilitate cellular uptake of various molecular cargoes, and one well known example is TAT peptide from HIV-1 TAT protein. In this study, recombinant plasmids were constructed and transformed into Escherichia coli strain BL21 (DE3) to express TAT-VP28, VP28, TAT-VP28-EGFP and VP28-EGFP fusion proteins. Enzyme-linked immunosorbent assay (ELISA) and flow cytometry methods were used to confirm that TAT fusion proteins can translocate from the intestine to the hemolymph of the crayfish Cambarus clarkii. After immunization, activities of phenoloxidase and superoxide dismutase were analyzed, and it was found that rTAT-VP28 produced the most pronounced increase in both C. clarkii were vaccinated by oral administration of rTAT-VP28 and rVP28 for 7 and 14 days, and rTAT-VP28 resulted in the highest relative percent survival (RPS) (63.3% at 7 days, and 67.8% at 14 days), compared with rVP28 (44.4% at 7 days, and 53.6% at 14 days) following challenge with WSSV after the last day of feeding. This study reports the use of TAT-derived peptide as an oral delivery method of a subunit vaccine against WSSV in C. clarkii.

Life-History Notes on Cambarus hubbsi Creaser (Hubbs Crayfish) from the South Fork Spring River, Arkansas

Many crayfish species native to the southeastern United States are imperiled due to small range sizes and anthropogenic impacts such as habitat loss and introduction of non-native species. Furthermore, effective management of crayfish is limited by the scarcity of life-history and ecological data for many of these species. We report results of the first life-history study of the crayfish Cambarus hubbsi (Hubbs Crayfish). We collected 466 Hubbs Crayfish from the South Fork Spring River, AR throughout 2006 and recorded carapace lengths, wet weights, indicators of reproductive activity, and number of eggs on ovigerous females. Using length-frequency distributions, we identified four Hubbs Crayfish age classes and evaluated growth rates by plotting size by season (winter, spring, summer, autumn). Male Hubbs Crayfish were more common than females in all seasons except autumn, and males weighed more at equivalent lengths than females. Reproductive activity in Hubbs Crayfish peaked in late winter and spring, and ovigerous females were collected in March, April, and June. Ovigerous females were age II or III and carried few eggs relative to co-occurring crayfish of the genus Orconectes. Compared to these Orconectes species, Hubbs Crayfish is comparatively slow growing, long lived, with low reproductive potential, and as a result may be categorized as a K life-history strategist. Based on this species' life-history strategy and previously documented habitat specificity and taxonomic distinctiveness, Hubbs Crayfish may require monitoring and management attention normally reserved for species with smaller ranges.

Influence of Elevated Temperature and Acid Mine Drainage on Mortality of the Crayfish Cambarus bartonii

ABSTRACT Effects of elevated temperature and acid mine drainage (AMD) on crayfish mortality were investigated in the Stony River, Grant County, West Virginia. During summers 2003 and 2004, four-week in situ bioassays were performed along a thermal and AMD gradient with the native crayfish Cambarus bartonii. Crayfish mortality was analyzed in conjunction with temperature and AMD related variables (pH, specific conductivity). Mortality was significantly higher (48–88%) at sites with high temperatures during 2003 (max = 33.0°C), but no significant differences were observed in 2004 (max = 32.0°C). Temperatures were higher in 2003 than 2004 due to increased discharge from a cooling reservoir flowing into the river. Additionally, duration of high temperature was approximately four days in 2003 as compared with only one day in 2004. No significant relationship between acid mine drainage variables and crayfish mortality was apparent.

Distribution and First Records of Branchiobdellida (Annelida: Clitellata) from Crayfishes (Crustacea: Decapoda) in the Maritime Provinces of Canada

Abstract Preserved specimens of the crayfish Cambarus bartonii, Orconectes limosus, and Orconectes virilis from 27 locations in New Brunswick, and O. limosus from Freshwater Lake, Cape Breton Highlands National Park, Cape Breton Island, NS, Canada, were examined for branchiobdellidans. Three species of branchiobdellidans—Bdellodrilus illuminatus, Cambarincola fallax, and Xironogiton instabilis—were identified on C. bartonii. Only branchiobdellidan cocoons were recorded on O. limosus, and only X. instabilis was recovered from O. virilis in New Brunswick. The introduction of O. limosus and O. virilis into New Brunswick does not appear to have simultaneously introduced non-native branchiobdellidans. No branchiobdellidans were found on introduced O. limosus from Freshwater Lake, NS. This work provides the first records of branchiobdellidans occurring in the Maritime Provinces of Canada, and establishes the eastern limit for these ectosymbionts in North America. In addition, one specimen of C. bartonii was fou...

Isotopic evidence for methane-based chemosynthesis in the Upper Floridan aquifer food web

Anecdotal observations of the Dougherty plain cave crayfish (Cambarus cryptodytes), the Georgia blind cave salamander (Haideotriton wallacei), and albinistic isopods (Caecidotea sp.) at great depths below the land surface and distant from river corridors suggest that obligate aquifer-dwelling (troglobitic) organisms are widely distributed throughout the limestone Upper Floridan aquifer (UFA). One mechanism by which subterranean life can proliferate in an environment void of plant productivity is through a microbial food web that includes chemosynthesis. We examined this possibility in the UFA by measuring the isotopic composition ((13)C, (14)C, and (15)N) of tissues from troglobitic macrofauna. Organisms that were captured by cave divers entering into spring conduits had delta(13)C values that suggested plant matter as a primary food resource (cave crayfish, -24.6 +/- 2.7 per thousand, n = 9). In contrast, delta(13)C values were significantly depleted in organisms retrieved from wells drilled into areas of the UFA remote from spring and sinkhole conduits (cave crayfish -34.7 +/- 9.8 per thousand, n = 10). Depleted (13)C values in crayfish were correlated with radiocarbon (Delta(14)C) depletion relative to modern values. The results suggest that methane-based microbial chemosynthetic pathways support organisms living in the remote interior of the aquifer, at least in part.

Host preference by an aquatic ectosymbiotic annelid on 2 sympatric species of host crayfishes

Abstract Symbiotic interactions can affect populations, communities, and ecosystems by creating novel flows of material and energy in food webs. However, there is considerable variability in host specificity among symbionts. We examined the host specificity of an ectosymbiotic annelid worm (Annelida:Clitellata:Branchiobdellidae) on 2 sympatric species of host crayfishes. In host-selection experiments, the branchiobdellid Cambarincola ingens colonized the crayfish Cambarus chasmodactylus 2.5x more frequently than similarly sized Orconectes cristavarius even though O. cristavarius was 2 to 4x more abundant in the field. Infestation intensity–body size regressions for Cambarincola in the New River reflected host-selection experiment results; the slopes for C. chasmodactylus were up to 8x steeper than those for O. cristavarius. In addition, 96% of C. chasmodactylus had at least one attached Cambarincola compared to only 36% for O. cristavarius. There are many possible explanations for the observed host prefer...