Description of a new species of cryptic snubnose darter (Percidae: Etheostomatinae) endemic to north-central Mississippi

Many subclades within the large North American freshwater fish genus Etheostoma (Percidae) show brilliant male nuptial coloration during the spring spawning season. Traditionally, perceived differences in color were often used to diagnose closely related species. More recently, perceived differences in male nuptial color have prompted further investigation of potential biodiversity using genetic tools. However, cryptic diversity among Etheostoma darters renders male nuptial color as unreliable for detecting and describing diversity, which is foundational for research and conservation efforts of this group of stream fishes. Etheostoma raneyi (Yazoo Darter) is an imperiled, range-limited fish endemic to north-central Mississippi. Existing genetic evidence indicates cryptic diversity between disjunctly distributed E. raneyi from the Little Tallahatchie and Yocona river watersheds despite no obvious differences in male color between the two drainages. Analysis of morphological truss and geometric measurements and meristic and male color characters yielded quantitative differences in E. raneyi from the two drainages consistent with genetic evidence. Morphological divergence is best explained by differences in stream gradients between the two drainages. Etheostoma faulkneri, the Yoknapatawpha Darter, is described as a species under the unified species concept. The discovery of cryptic diversity within E. raneyi would likely not have occurred without genetic tools. Cryptic diversity among Etheostoma darters and other stream fishes is common, but an overreliance on traditional methods of species delimitation (e.g., identification of a readily observable physical character to diagnose a species) impedes a full accounting of the diversity in freshwater fishes in the southeastern United States.

Estimating thermal response metrics for North American freshwater fish using Bayesian phylogenetic regression

Physiological performance in fish peaks within a well-defined range of temperatures, which is distinct for each species. Species-specific thermal responses for growth, survival, and reproduction are most commonly quantified directly through laboratory experiment or field observation, with a focus on six specific metrics: optimum growth temperature and final temperature preferendum (growth), upper incipient lethal temperature and critical thermal maximum (survival), and optimum spawning temperature and optimum egg development temperature (reproduction). These values remain unknown for many North American freshwater fish species. In this paper, we present a new statistical method (Bayesian phylogenetic regression) that uses relationships between these metrics and phenetic relatedness to estimate unknown metric values. The reliability of these estimates was compared with those derived from models incorporating taxonomic family and models without any taxonomic information. Overall, incorporating taxonomic family relatedness improved estimation accuracy across all metrics. For Salmonidae and Cyprinidae, estimates derived from Bayesian phylogenetic regression typically had the highest expected reliability. We used our methods to generate 274 estimates of unknown metric values for over 100 North American freshwater fish species.

Large-scale changes in the littoral fish communities of lakes in southeastern Ontario, Canada

Biodiversity loss is a serious issue for freshwater fishes in temperate climates and there is a need for more information in this area. A study was conducted to assess fish community changes in the littoral zone of 22 lakes over a 45 year period (compared years 1969–1979 and year 2014). To compare fish communities, historical seining records were compiled for 22 inland lakes and compared with contemporary data sampled using the same protocol. Fish abundance data analyzed using a multivariate approach identified a shift from cyprinid-dominated communities to centrarchid-dominated communities between time periods. There was no evidence to support a strong influence of invasive species on these communities, but there have been significant changes in temperature and land use around these lakes since the historical data sets were collected. This is an important contribution to our understanding of biodiversity change in North American freshwater fish communities and may influence fisheries management approaches in the future.

Phylogeny influences the relationships linking key ecological thermal metrics for North American freshwater fish species

Habitat temperature is a major determinant of performance and activity in fish. We summarize published studies of 173 North American freshwater fish species to examine the interrelationships among thermal response metrics associated with three types of individual performance: growth (optimal growth temperature (OGT), final temperature preferendum (FTP)), survival (upper incipient lethal temperature (UILT), critical thermal maximum (CTMax)), and reproduction (optimum spawning temperature (OS), optimum egg development temperature (OE)). We found that all metrics were highly correlated, especially those associated with a specific performance type. Differences in thermal metrics were also significantly linked to traditional thermal guild classifications, spawning season, and strategy. We found an overall decline in correlation strength when we used phylogenetically independent contrasts to control for the effect of phylogeny. This decline was much greater for growth and survival metrics than for reproduction. This suggests that the role of evolutionary history in determining thermal sensitivity at the species level varies greatly across the range of performance types that can be used to characterize the behaviour of an individual.

The discovery of progenetic Allocreadium neotenicum Peters, 1957 (Digenea: Allocreadiidae) in water beetles (Coleoptera: Dytiscidae) in Great Britain

Progenetic specimens of Allocreadium neotenicum Peters, 1957 are described from water beetles, Hydroporus rufifrons, an endangered species, and Agabus paludosus from northern England and Scotland, and as non-ovigerous metacercariae from Agabus melanarius from southern England. Morphologically, the worms are identical to A. neotenicum described from water beetles in North America. Molecular phylogenetic estimates based on 28S rDNA sequences show these British specimens as more closely related to the North American freshwater fish parasite Allocreadium lobatum Wallin, 1909 than to the European species A. isoporum (Looss, 1894). A. lobatum shows a predilection for progenesis and may be a senior synonym of A. neotenicum. Based on the molecular phylogeny, the genus Pseudallocreadium Yamaguti, 1971 is considered synonymous with Allocreadium and the two species assigned to that genus, P. neotenicum and P. alloneotenicum (Wootton, 1957) are returned to Allocreadium.