Stephen J. Jacquemin

Cryptic phenotypic plasticity in populations of the freshwater prosobranch snail, Pleurocera canaliculata

We sampled four populations of the robustly shelled Pleurocera canaliculata from large rivers and five pleurocerid populations bearing more fusiform shells (nominally P. acuta and P. pyrenellum) from smaller streams in a study area extending from upstate New York to northern Alabama, USA. Gene frequencies at 9 allozyme-encoding loci revealed that each population of P. acuta or P. pyrenellum was more genetically similar to the P. canaliculata population inhabiting the larger river immediately downstream than to any nominal conspecific. Thus, the extensive intraspecific variation in shell robustness displayed by these nine populations has apparently been rendered cryptic by taxonomic confusion. We then employed geometric morphometrics to explore a gradient in shell morphology from the acuta form to the typical canaliculata form in 18 historic samples collected down the length of Indiana’s Wabash River. The shell forms appeared generally distinctive on the major axes yielded by relative warp analysis (increasing robustness and decreasing spire elongation), although some overlap was apparent. MANCOVA returned a significant relationship between multivariate shape variation and stream size, as measured by drainage area. Possible drivers for this phenomenon include an environmental cline in the risk of dislodgement due to hydrodynamic drag and shifts in the community of predators.

Morphology of Elimia livescens (Mollusca: Pleuroceridae) in Indiana, U.S.A. Covaries with Environmental Variation

Abstract: We examined covariation of morphology with local and regional environmental variables in the widespread North American freshwater gastropod Elimia livescens (Menke, 1830). Geometric morphometrics was used to quantify shape of individuals collected at sites in Indiana, U.S.A. We used the Procrustes superimposition method and relative warp analysis to examine variation among individuals. We found that shape of E. livescens covaried significantly with flowing versus non-flowing habitats, drainage area, latitude and longitude, water temperature, conductivity, substrate type, and the presence of woody debris. Individuals with smaller apertures and streamlined shape occurred in smaller watersheds in the southeastern regions of Indiana, and in local habitats with low water flow, low conductivity, large, coarse substrate (rip-rap), low frequency of woody debris, and higher dissolved oxygen. We suggest that morphological variation is an integral part in maintaining a wide distribution and maximizing local success for an aquatic gastropod that occurs in a variety of environments.

Body size and geographic range do not explain long term variation in fish populations: a Bayesian phylogenetic approach to testing assembly processes in stream fish assemblages.

We combine evolutionary biology and community ecology to test whether two species traits, body size and geographic range, explain long term variation in local scale freshwater stream fish assemblages. Body size and geographic range are expected to influence several aspects of fish ecology, via relationships with niche breadth, dispersal, and abundance. These traits are expected to scale inversely with niche breadth or current abundance, and to scale directly with dispersal potential. However, their utility to explain long term temporal patterns in local scale abundance is not known. Comparative methods employing an existing molecular phylogeny were used to incorporate evolutionary relatedness in a test for covariation of body size and geographic range with long term (1983 – 2010) local scale population variation of fishes in West Fork White River (Indiana, USA). The Bayesian model incorporating phylogenetic uncertainty and correlated predictors indicated that neither body size nor geographic range explained significant variation in population fluctuations over a 28 year period. Phylogenetic signal data indicated that body size and geographic range were less similar among taxa than expected if trait evolution followed a purely random walk. We interpret this as evidence that local scale population variation may be influenced less by species-level traits such as body size or geographic range, and instead may be influenced more strongly by a taxon’s local scale habitat and biotic assemblages.

Wabash River Freshwater Drum Aplodinotus grunniens Diet: Effects of Body Size, Sex, and River Gradient

Abstract The objectives of this study were to describe the diets of freshwater drum Aplodinotus grunniens in the Wabash River in the Midwestern United States. We used a multivariate ordination approach (nonmetric multidimensional scaling) to describe drum diets combined with a generalized linear model to test for covariation of diet with body size, sex, and longitudinal river gradient. Hydropsychidae (trichoptera, caddisfly larvae), pleuroceridae (gastropoda), and heptageniidae (ephemeroptera, mayfly larvae) were the most consumed prey items (∼75% of overall diets). Among all freshwater drum, hydropsychidae, pleuroceridae, and heptageniidae were present in 69%, 23%, and 38% of stomachs, respectively. Freshwater drum diets were similar along an upstream–downstream river gradient spanning 350 river km, but varied with body size and sex. Small- and medium-sized fish tended to consume more diptera and annelids compared with the largest individuals, which fed on mollusks and crayfish. With control for body siz...

Effects of water velocity on the size and shape of rusty crayfish, Orconectes rusticus

Abstract.  Phenotypic plasticity of ecologically relevant traits relating to physiology, behavior, morphology, and life history is widespread and can affect the ecology and evolution of organisms. In streams, phenotypic plasticity in morphology and corresponding differences in performance have been documented for fishes and, to a lesser extent, for macroinvertebrates. Morphological plasticity in crayfish has not been addressed but, if present, has the potential to interact with behaviorally plastic traits to affect performance in high water velocities. Lake and stream invasions of rusty crayfish, Orconectes rusticus, provide excellent opportunities to examine morphological variation in habitats differing in water velocity. Spread of O. rusticus and displacement of resident species in lakes has been attributed to larger mean body and chelae sizes than for native species, but larger body and chelae sizes may not be advantageous in high-velocity environments. We examined populations of male O. rusticus (form I and II) from lakes, low-velocity streams (LVS ≈ 25 cm/s), and high-velocity streams (HVS ≈ 50 cm/s) to test the hypothesis that size and shape are affected by water velocity. We analyzed scanned images of chelae and body with geometric morphometrics. Body size differed significantly between HVS populations and LVS and lake populations, which did not differ in size or shape. Shape tended to differ between HVS populations and LVS and lake populations. Chelae of form I but not of form II crayfish were significantly smaller in HVS than in LVS and lake populations. Chelae (form I and II) in HVS populations were broader and stunted relative to chelae in LVS and lake populations. Chelae may help deflect water over the bodies. Morphological plasticity in crayfish adapted to HVS may alter invasion rate or success with subsequent effects on stream ecosystems.

Morphology of Bluntnose Minnow Pimephales Notatus (Cyprinidae) Covaries with Habitat in a Central Indiana Watershed

Morphological variation of taxa frequently is correlated with local environmental variation. We tested for covariation in morphology and environmental variables in bluntnose minnow Pimephales notatus from 10 sites in central Indiana. We used principal components analysis (PCA) to summarize local environmental variation and geomorphic morphometrics (procrustes method and relative warp analysis) to summarize morphological variation among individuals. We used MANCOVA to test for variation in morphology attributable to environmental variation, body size, and sexual dimorphism. Additionally, we used linear discriminant analysis (LDA) to identify if morphology varies with sexual dimorphism. Individual relative warp scores were separated by sex and tested for covariation with habitat PC axes using Pearsons correlations. We identified shape variation that was correlated with environment irrespective of body size or sex. Individuals with deeper-bodies tended to occur in deeper and wider streams with increased discharge. Individuals with fusiform body shape (e.g., slender elongated snouts) tended to occur at sites with increased current velocity. Although the morphology of male and female individuals covaried similarly with environmental variation, LDA significantly distinguished females, which had distended abdomens, narrower caudal peduncle and dorsal fin bases, and slightly upturned head shapes compared to males. We suggest that shape variation may be a product of phenotypic plasticity and may contribute toward the success of species with broad physicochemical tolerances by enhancing their ability to occupy a wide range of hydrological conditions.

Evolution of mating systems and sexual size dimorphism in North American cyprinids

Mating systems evolve with sexual size dimorphism (SSD) in many animals. Mating systems with males larger than females occur when males compete for female access or guard territories, while mating systems with group mating tend to occur in species where females are the same size or larger than males. In addition to variation in SSD with mating system, sperm competition varies among mating systems in predictable patterns. We examined the evolution of mating systems with SSD and testes mass in 111 North American Cyprinidae fishes using phylogenetic comparative methods. Our results demonstrate that the evolution of mating systems in Cyprinidae fishes is from ancestral taxa that are group spawners with females the same size or larger than males to pair spawning systems where males tend to be larger than females. We used an additive model to predict male and female body size from testes mass and mating system. Only mating system varied predictably with SSD. Our results for analyses of hyperallometry (Rensch’s rule) were that individual species of Cyprinidae can have hyperallometry for SSD, but the pattern is not present across all taxa.

The Heritability of Shell Morphometrics in the Freshwater Pulmonate Gastropod Physa

The cosmopolitan freshwater pulmonate snail Physa acuta hybridizes readily with Physa carolinae in the laboratory, although their F1 progeny are sterile. The two species differ qualitatively in shell shape, the former bearing a more globose shell and the latter more fusiform. We performed a hybridization experiment, measuring a set of 14 traditional (linear) and landmark-based shell morphological variables on even-aged parents and their offspring from both hybrids and purebred control lines. Parent-offspring regression yielded a strikingly high heritability estimate for score on the first relative warp axis, h2 = 0.819 ± 0.073, a result that would seem to confirm the value of geometric morphometrics as a tool for retrieving evolutionary relationships from gastropod shell form. Score on the second relative warp axis was also significantly heritable (h2 = 0.312 ± 0.123), although more moderate, as were scores on second principal components extracted from traditional measurements (correlation h2 = 0.308 ± 0.069, covariance h2 = 0.314 ± 0.050). Although score on the first relative warp axis was significantly correlated with centroid size (p < 0.001), scores on none of the three second axes were so correlated. This result suggests that second axis score might prove especially useful for estimating genetic divergence among mixed-age populations of gastropods sampled from the field.

Effects of flow regime on growth rate in freshwater drum, Aplodinotus grunniens

Understanding the influence of flow regime hydrology on fish life history is essential for conservation and management of lotic ecosystems. The objectives of this study were to investigate growth patterns of Wabash River freshwater drum Aplodinotus grunniens relative to age, sex, and long term flow regime variation. Growth was estimated using back-calculated lengths from otolith measurements. Flow regime was described using Indicators of Hydrologic Alteration flow metrics calculated from long-term stream flow data at USGS stations. A generalized linear mixed model was used to model growth as a function of age, sex, and flow regime. Freshwater drum growth was explained by variation in age, sex, and flow magnitude. Freshwater drum exhibited indeterminate growth relative to age. Mean growth rates and mean length at age were lower in males than females. High magnitude flow events were positively correlated with increased growth rates in both males and females. However, the effect of flow magnitude variation on growth was stronger in males. The primary flow regime metrics related to growth were magnitude-based and were not related to timing of flow events. The study provides evidence that long term variation in flow regime is a catalyst for alterations in freshwater drum growth rates.

Habitat Variation Among Aquatic Gastropod Assemblages of Indiana, USA~!2008-11-19~!2008-12-24~!2009-01-22~!

We collected aquatic gastropods at 137 sites in lakes and streams of Indiana and tested for patterns of assem- blages with environmental variables. The survey resulted in 32 species with a mean of 2.8 species at each site, and a mean abundance at each site of 144 individuals. Nonmetric multidimensional scaling (NMS) multivariate analyses resulted in watershed drainage area, water conductivity, substrate category frequency, and dissolved oxygen as significant correlates of gastropod assemblage structure. Gastropod assemblages of lakes were not significantly different than assemblages of streams in the ordination. Prosobranch taxa occurred in higher abundances than pulmonate taxa at sites with lower con- ductivity in larger watersheds. There were no pairs of gastropod species that tended to co-occur more frequently than ran- dom. Our analyses resulted in local environmental variables providing explanation of aquatic gastropod assemblage struc- ture.