Fundulus Notatus Research Articles

Variable rates of hybridization among contact zones between a pair of topminnow species, Fundulus notatus and F. olivaceus.

Pairs of species that exhibit broadly overlapping distributions, and multiple geographically isolated contact zones, provide opportunities to investigate the mechanisms of reproductive isolation. Such naturally replicated systems have demonstrated that hybridization rates can vary substantially among populations, raising important questions about the genetic basis of reproductive isolation. The topminnows, Fundulus notatus and F. olivaceus, are reciprocally monophyletic, and co-occur in drainages throughout much of the central and southern United States. Hybridization rates vary substantially among populations in isolated drainage systems. We employed genome-wide sampling to investigate geographic variation in hybridization, and to assess the possible importance of chromosome fusions to reproductive isolation among nine separate contact zones. The species differ by chromosomal rearrangements resulting from Robertsonian (Rb) fusions, so we hypothesized that Rb fusion chromosomes would serve as reproductive barriers, exhibiting steeper genomic clines than the rest of the genome. We observed variation in hybridization dynamics among drainages that ranged from nearly random mating to complete absence of hybridization. Contrary to predictions, our use of genomic cline analyses on mapped species-diagnostic SNP markers did not indicate consistent patterns of variable introgression across linkage groups, or an association between Rb fusions and genomic clines that would be indicative of reproductive isolation. We did observe a relationship between hybridization rates and population phylogeography, with the lowest rates of hybridization tending to be found in populations inferred to have had the longest histories of drainage sympatry. Our results, combined with previous studies of contact zones between the species, support population history as an important factor in explaining variation in hybridization rates.

Fundulus notatus

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A Black Spot on Our Record: Invasion History of the Nonnative Blackspotted Topminnow (Fundulus olivaceus) in the Spring River Subbasin of Kansas, with a Comparison to Long-Term Trends in Prevalence of Blackstripe Topminnow (Fundulus notatus)

The Blackspotted Topminnow (Fundulus olivaceus) is not native to the Spring River subbasin (SRS) of Kansas, where it was first collected from Shoal Creek in the early 2000s. To date, little is known concerning the contemporary prevalence of Blackspotted Topminnow in the SRS of KS, or how prevalence of the closely related Blackstripe Topminnow (Fundulus notatus) in the SRS has varied since Blackspotted Topminnow invaded this system. To evaluate the contemporary prevalence of the Blackspotted Topminnow in the KS SRS, we sampled 55 sites using backpack electrofishing and seining during 2017-2020. We then compared long-term trends in occupancy and relative abundance of the Blackspotted and Blackstripe Topminnows in the KS SRS using four separate datasets collected during 1962-1964, 1993-1995, 1995-2013, and our contemporary dataset from 2017-2020. Between species comparisons of temporal trends were made for the entire SRS of KS, and for physiographic regions within the SRS that differed in habitat characteristics and Blackspotted Topminnow presence. In our contemporary survey, we detected the Blackspotted Topminnow at 11% of sites (6/55), including four Shoal Creek sites and two sites in the Spring River below Empire Lake. Blackstripe Topminnow prevalence was relatively stable in the SRS during 1962-2020, where it was most widespread and abundant within streams of the Cherokee Lowlands and Osage Cuestas. In contrast, between the 1995-2013 and 2017-2020 time periods Blackstripe Topminnow exhibited a declining trend in prevalence within the Ozark Plateau where it was sympatric with the Blackspotted Topminnow. This decline was not observed in the Ozark Plateau where Blackspotted Topminnow was absent. Declining Blackstripe Topminnow prevalence may be due to negative biotic interactions (e.g., competition; hybridization) with the Blackspotted Topminnow, or could be the result of unquantified environmental variation. Regardless, our research showed that the Blackspotted Topminnow is now an established nonnative in the SRS of KS. Consequently, further research of this species is necessary to determine how the invasion process proceeds regarding continued spread and potential concomitant ecological impacts.

Late Pleistocene range expansion of North American topminnows accompanied by admixture and introgression

AbstractAimWe used genome‐scale sampling to assess the phylogeography of a group of topminnows in the Fundulus notatus species complex. Two of the species have undergone extensive range expansions resulting in broadly overlapping distributions, and sympatry within drainages has provided opportunities for hybridization and introgression. We assessed the timing and pattern of range expansion in the context of late Pleistocene–Holocene drainage events and evaluated the evidence for introgressive hybridization between species.LocationCentral and southern United States including drainages of the Gulf of Mexico Coastal Plain and portions of the Mississippi River drainage in and around the Central Highlands.TaxonTopminnows, Genus Fundulus, subgenus Zygonectes—Fundulus notatus, Fundulus olivaceus, Fundulus euryzonus.MethodsWe sampled members of the F. notatus species complex throughout their respective ranges, including numerous drainage systems where species co‐occur. We collected genome‐wide single nucleotide polymorphisms (SNPs) using the genotype‐by‐sequencing (GBS) method and subjected data to population genetic analyses to infer the population histories of both species, including explicit tests for admixture and introgression. The methods employed included STRUCTURE, principal coordinates analysis, TreeMix and approximate Bayesian computation.ResultsGenetic data are presented for 749 individuals sampled from 14 F. notatus, 20 F. olivaceus and 2 F. euryzonus populations. Members of the species complex differed in phylogeographic structure, with F. notatus exhibiting geographic clusters corresponding to Pleistocene coastal drainages and F. olivaceus comparatively lacking in phylogeographic structure. Evidence for interspecific introgression varied by drainage.Main conclusionsPopulations of F. notatus and F. olivaceus exhibited contrasting patterns of lineage diversity among coastal drainages, indicating interspecific differences in their Pleistocene southern refugia. Phylogeographic patterns in both species indicated that range expansions into the northern limits of contemporary distributions coincided with and continued subsequent to the Last Glacial Maximum. There was evidence of introgression between species in some, but not all drainages where the species co‐occur, in a pattern that is correlated with previous estimates of hybridization rates.

A habitat-based framework to predict the effects of agricultural drain maintenance on imperiled fishes

One third of the total global land viable for agricultural production has artificial drainage systems. These drainage systems can provide important habitat for fishes and, in some cases, imperiled fish species vulnerable to impact by drainage maintenance activities. A framework to provide quantitative assessments of the effects of maintenance activities on imperiled fish species is needed. In this study, a six-step habitat-based framework was developed to predict suitable habitat for two at-risk species in an agricultural drain: the Endangered Pugnose Shiner (Notropis anogenus) and the Special Concern Blackstripe Topminnow (Fundulus notatus). Using the framework, spatial models were developed to assess the effects of proposed drain maintenance on the overall amount of suitable habitat, habitat patch size, and connectivity of habitat patches. Maintenance had a significant impact on habitat connectivity, but did not significantly reduce the habitat size of isolated patches. The amount of suitable habitat available after maintenance fell below the minimum area for population viability (MAPV) for the Pugnose Shiner, but not the Blackstripe Topminnow. Future impact assessments of drain maintenance should incorporate population viability analysis, coupled with habitat patch analysis (patch size and connectivity), to quantitatively test consequences of proposed alteration to the viability of spatially structured populations.

Helminth Parasites of the Blackstripe Topminnow,Fundulus notatus(Cyprinodontiformes: Fundulidae), from Arkansas and Oklahoma, U.S.A.

ABSTRACT: Between August 2014 and August 2015, in the Ouachita and Red River drainages of Arkansas (n = 17) and the Red River drainage of Oklahoma (n = 113), 130 Blackstripe Topminnows, Fundulus notatus, were collected and examined for helminth parasites. Sixty-three (48%) F. notatus, including 7 (37%) from Arkansas and 56 (50%) from Oklahoma, were infected. These included 16 (12%) with Homalometron robisoni, 24 (18%) with immature Proteocephalus sp., 8 (6%) with larval Eustrongylides sp., 17 (13%) with Spiroxys sp. larvae, 3 (2%) with acanthocephalan cystacanths, 1 (0.8%) with Leptorhynchoides thecatus, and 1 (0.8%) with Neoechinorhynchus sp. In addition, 1 of 5 (20%) from Arkansas harbored the monogenean Salsuginus umbraensis. We document 4 new host and 3 new distributional records.

Hybridization and introgression in two ecologically dissimilar Fundulus hybrid zones.

Hybridization and introgression appear more common in rapidly evolving groups, suggesting an important role in the evolutionary process. Detailed studies of how extrinsic or intrinsic forces regulate hybridization and introgression have the potential for broadening our understanding of mechanisms generating diversity. Species in the Fundulus notatus species complex have broad overlapping ranges and occur in replicated hybrid zones along predictable stream gradients. Typical hybrid zone structure has Fundulus olivaceus in headwaters, F. notatus downstream, and hybrid zones near confluences or abrupt shifts in habitat. Rarely, the typical upstream-downstream orientation is reversed raising questions as to how hybrid zones are formed and maintained. We used next-generation sequencing data to study hybridization and introgression in hybrid zones in neighboring drainages that differ in orientation (typical and reversed). We predicted extrinsic forces linked to stream gradients would result in noticeable differences between the two. Contrary to predictions, the data indicate the hybrid zones are remarkably similar. We used individual-based simulations to explore the potential role of intrinsic and extrinsic forces in generating and maintaining typical and reversed hybrid zones. Simulation results were consistent with reversed hybrid zones being formed from stochastic processes combined with strong intrinsic forces and weak extrinsic forces.

Jamie Edward Thomerson (1935–2015)

J AMIE EDWARD THOMERSON, Ichthyologist and Professor Emeritus, Department of Biological Sciences, Southern Illinois University–Edwardsville (SIU-E), passed away quietly on 4 January 2015, in Austin, Texas, after a two-year battle with prostate cancer (Fig. 1). He is survived by his wife of 57 years, Kathleen Thomerson, his sons Austin and Eric Thomerson, his daughter Rachel Miller, a son-in-law Richard Miller, and a grandson Mason Miller. Jamie, or “Jim,” was a Texan and a country boy, and he was proud of both. He was born on 7 May 1935 in Menard, a small town in the Texas Hill Country. He grew up in that part of the world, as did his father and grandfather. Jim was the only child of Eula Lee (Martin) (1902–1998) and Roy Thomerson (1898–1976). Eula was a teacher until her marriage to Roy in 1926. In 1936, shortly after Jim’s birth, they purchased a ranch, the Old Walston Place, south of Menard and operated it as a goat and cattle ranch. In his adult life, Jim often amused students and friends by recounting stories about life on the ranch. One favorite tale described how his mother would regularly take the rifle out into their woods to hunt squirrels, which she then cleaned and fried, made gravy, and served as the family dinner. As a boy, Jim was tasked by his parents to complete a variety of ranch chores, for instance, burning the thorns off cacti so that the goats could more easily feed on the plants, and using a rifle to control ground squirrels and armadillos. The family ranch was also where Jim became fascinated with the natural world. He wandered the ranch and explored nearby streams and became enchanted with the native fish faunas. Young Jim was also an avid reader and was especially enthralled by the exploits of Edgar Rice Burroughs’ characters, Tarzan, John Carter, and Carson Napier. Jim graduated fromMenard High School in 1953 and then enrolled in the University of Texas where he majored in geology, earning a B.S. in 1957. While an undergraduate, Jim met fellow Texas student Kathleen Armstrong and the two married in Austin on 1 June 1957. Kathleen is a musician, having studied in Europe with the renowned composers and organists Jean Langlais in Paris and Flor Peeters in Antwerp. She subsequently distinguished herself professionally and academically as a church and concert organist, organ instructor, book author, and composer of widely played hymns. After military service in the National Guard, Jim taught biology and chemistry classes at Electra High School in Electra, Texas, for the 1958–59 school year. He then entered the graduate program at Texas Tech University in Lubbock where he conducted research in micropaleontology (Forminifera and Ostracoda), obtaining his M.S. in Geology in 1961. Still in his mid-20s, Jim decided to shift from geology to biology and was accepted into the graduate program at Tulane University. Jim’s wife Kathleen remembers their life in New Orleans with special fondness. At Tulane, Jim researched the hybridization, geographical variation, and distribution of the topminnows Fundulus notatus and F. olivaceus under the guidance of the legendary ichthyologist Royal D. Suttkus. Contemporary Suttkus students at Tulane during Jim’s tenure included Clyde Barbour, Glenn Clemmer, Salvador Contreras Balderas, and John Ramsey. Of course, being a Suttkus student involved intensive collection trips in the southeastern United States (Fig. 2). The Tulane Fish Collection houses specimens from 31 collections made by Jim in Fig. 1. Jamie E. Thomerson, 2011. Photo courtesy of Kathleen Thomerson.

Two New Species of Homalometron (Digenea: Apocreadiidae) from Nearctic Freshwater Fundulids, Elucidation of the Life Cycle of H. cupuloris, and Molecular Phylogenetic Analysis of Some Congeners.

Two species of digeneans belonging in Homalometron are described from Nearctic freshwater fundulid fishes: Homalometron robisoni n. sp. is described from the Blackstripe Topminnow, Fundulus notatus, from Oklahoma and Homalometron frocioneae n. sp. is described from the Banded Killifish, Fundulus diaphanus, from New York. Homalometron robisoni n. sp. differs from all congeners by having vitelline follicles that extend into the forebody, a feature that necessitates altering the generic diagnosis for the genus. Homalometron frocioneae n. sp. may be distinguished from North and Middle American congeners by the position of the intestinal bifurcation (relatively more posterior in the forebody than in other species) and tegumental spine coverage on the body (spines are absent from the posterior body extremity and on most of the dorsal surface). Comparison of ribosomal DNA (ITS 1 and 2 regions, 5.8S gene, and partial fragment of 28S gene) from the 2 new species and some congeners from the Western Hemisphere provided evidence for the validity of the 2 new species and affirmed a close relationship between H. robisoni n. sp. and Homalometron pallidum. Comparison of ribosomal DNA from newly collected Homalometron spp. and larval stages of an apocreadiid from brackish water hydrobiid snails (cercariae in rediae in Littoridinops palustris and metacercariae in L. palustris and Amnicola limosa ) from a tidal river in Mississippi revealed that larval stages represented Homalometron cupuloris. A phylogeny based on Bayesian inference analysis using partial 28S rDNA gene fragments from 14 species of Homalometron (all from the Western Hemisphere) and 1 megaperine and rooted by a second megaperine was conducted and produced a strongly supported phylogram that estimates the interrelationships among species. The estimated phylogeny suggests that ecological factors such as salinity and food web interactions between species of Homalometron, intermediate hosts, and fishes drive coevolutionary forces influencing speciation within Homalometron.

Influence of sex and habitat on the size and shape of anal and dorsal fins of the blackstripe topminnow Fundulus notatus.

The size and shape of the anal and dorsal fin in the blackstripe topminnow Fundulus notatus from lake and stream habitats across multiple ages and sexes were examined. Differences in the size and shape of anal and dorsal fins were sex-specific and not related to habitat differences. Males have longer and more pointed anal fins and longer, larger and more pointed dorsal fins than females. These sex differences occur predominantly in the older age class. The angle (i.e. pointedness) of the dorsal and anal fins is tightly correlated suggesting that fins follow a similar growth trajectory as individuals become sexually mature.

Isolation and characterization of microsatellite loci for the blackstripe topminnow Fundulus notatus and their variability in two closely related species.

A total of 17 polymorphic microsatellite loci were isolated from the blackstripe topminnow Fundulus notatus. In a sample of 29 individuals, these loci were found to possess two to 19 alleles with expected heterozygosity values ranging from 0.212 to 0.919 and all but one of the loci conformed to Hardy-Weinberg equilibrium expectations. Many of these loci were polymorphic in the closely related species Fundulus olivaceus and Fundulus euryzonus providing a set of markers that should prove useful in future ecological and evolutionary studies of members of this species complex.

An evaluation of multiple-pass seining to monitor blackstripe topminnow Fundulus notatus (Rafinesque, 1820) in the Sydenham River (Ontario, Canada)

Summary Multiple-pass (i.e. removal) sampling and mark-recapture experiments were undertaken in the Sydenham River (Ontario, Canada) to assess the effectiveness of seining to detect and estimate the local abundance of blackstripe topminnow, Fundulus notatus (Rafinesque, 1820) as well as to compare catch characteristics from closed and open (with and without block nets) sample units. Probability of species detection using three-pass seining was estimated to be 0.58 in closed units, and 0.51 in open units. To be 95% confident of occupancy status, a minimum of five repeat surveys is required. A decline in catch occurred in only half of the sample units, population size estimates were often imprecise, and attempts to generate mark-recapture population estimates were unsuccessful. Mean capture probabilities were 0.48 in closed units and 0.65 in open units, when depletion occurred. For blackstripe topminnow and other fishes encountered, there were no significant differences between closed and open units in the frequency of depletion or capture probability. Compared to single-pass surveys, monitoring programs that employ three seine hauls are more likely to detect the presence of the blackstripe topminnow and any decline in local abundance.

Developing Standardized Methods for Sampling Freshwater Fishes with Multiple Gears: Effects of Sampling Order versus Sampling Method

AbstractDeveloping robust methodologies for sampling freshwater fishes is important for the assessment and recovery of aquatic biodiversity. Commonly, sampling protocols recommend the use of both electrofishing and seining to reduce bias when sampling freshwater fishes. The objective of this study was to determine whether sampling method, sampling order, or the combination of these influenced the assessment of diversity and abundance of common or rare freshwater fishes at both the species and assemblage level. Fifty sites were sampled in the Sydenham River, Ontario, Canada, where paired sites were sampled using both electrofishing and seine netting in close proximity but also reversing the initial sampling order. Differences in the abundance and richness of common and rare freshwater fishes were tested with two‐way ANOVA and multivariate ANOVA. Multivariate differences in the representation of species assemblages were compared using Procrustes analysis across ordinations built using differences in sampling method and sampling order. Electrofishing outperformed seine netting for maximizing the abundance of both all species caught (P = 0.004) and only those species considered rare (P = 0.049). While capture efficiencies generally decreased with subsequent sampling, the interaction between sampling method and sampling order for maximizing richness estimates of rare species was significant (P = 0.049). There were important species and assemblage differences when sampling order was reversed. The representation of either sunfishes (family Centrarchidae) or catfishes (family Ictaluridae) differed in multivariate space, given different sampling order. In addition, the capture of Blackstripe Topminnow Fundulus notatus was enhanced when seine netting was used after electrofishing. This study highlights the often neglected aspect of choosing an appropriate sampling order when developing protocols for sampling freshwater fishes with multiple methods. Overall, the combination of electrofishing, followed by seine netting, appears to maximize capture efficiencies of both common and rare fishes; however, researchers should be aware that sampling order can alter the representation of species and assemblages in multivariate assessments.

The landscape genetics of syntopic topminnows (Fundulus notatusandF. olivaceus) in a riverine contact zone

The metapopulation dynamics of a species are influenced by the spatial arrangement of preferred habitats across a landscape. Increasing habitat patchiness can result in greater population subdivision, leading to more pronounced population genetic structure. Therefore, even subtle differences in habitat preferences among species could lead to substantial differences in genetic structure. Members of the Fundulus notatus species complex of topminnows include a headwater specialist and a large river specialist with broadly overlapping geographical distributions. Both species are often found in the same drainage systems, but partially isolated by divergent habitat preferences. The purpose of this research was to determine whether distribution along a stream continuum in a contact zone influences population genetic patterns in two species of topminnow (Fundulus olivaceus and Fundulus notatus). Fish were collected in the summers of 2010–2012, and habitat data were collected in summer 2012, within all major tributaries of the Saline River in southern Illinois. In total, 523 fish were genotyped using seven microsatellite loci to assess genetic variation. Species distributions in F. notatus and F. olivaceus were associated with habitat factors that covaried with cumulative drainage area. Populations of F. olivaceus showed a greater level of genetic structure reflected in a significant pattern of isolation by distance, while populations of F. notatus showed no such pattern. Spatial autocorrelation analysis revealed that at an individual level, both species became increasingly divergent with waterway distance. Overall, clear interspecific differences in habitat preferences were translated into measurable but relatively subtle differences in population genetic structure.

Contrasting phylogeographic histories between broadly sympatric topminnows in the Fundulus notatus species complex

Sympatrically distributed closely related species provide opportunities for studying evolutionary patterns of diversification. Such studies must account for historical contingencies in interpreting contemporary patterns of variation. Topminnows in the Fundulus notatus species complex are distributed sympatrically across much of the southern and Midwestern United States. Throughout most of their ranges F. olivaceus is often found in headwater stream habitats, and F. notatus is more typically distributed along the margins of larger river habitats. However, in some drainages, ecological associations of the respective species are reversed, with F. notatus populations isolated in headwater streams and F. olivaceus in downstream river habitats. Phylogeographic analyses of AFLP marker and multi-locus sequence data detected historical isolation in F. notatus consistent with pre-Pleistocene drainage patterns. Four F. notatus clades corresponded to (i) the Western Gulf Slope, (ii) the southwestern Ouachita Highlands, (iii) the Mobile Basin, and (iv) central Coastal Plain and Mississippi River Basin. In contrast, a relative lack of range-wide geographic structure in F. olivaceus is consistent with recent range expansion over much of the same geographic area. The southwestern Ouachita Highlands and Mobile Basin F. notatus clades corresponded to regions where ecological associations between the two species are reversed, providing evidence of the independent evolution of variation in contemporary habitat associations. Fundulus olivaceus from several drainages demonstrated introgression of mitochondrial DNA from F. notatus, but none of the sites in this study included individuals with hybrid ancestry in their nuclear genome. Phylogenetic analyses that included only nuclear loci supported the reciprocal monophyly of F. notatus, F. olivaceus and a third narrowly endemic species, Fundulus euryzonus, and supported a sister relationship between F. olivaceus and F. euryzonus.

Variation in contact zone dynamics between two species of topminnows, Fundulus notatus and F. olivaceus, across isolated drainage systems

Spatially variable selection pressure within heterogeneous environments can result in the evolution of specialist phenotypes that facilitate co-occurrence of closely related species and limit genetic exchange. If divergent selection pressures maintain reproductive isolation, hybridization is expected to correlate with the strength of underlying ecological gradients and the traits shaped by adaptive processes. We sampled ten replicate topminnow (Fundulus olivaceus and Fundulus notatus) hybrid zones in isolated drainages throughout central and southern North America. In all drainages, species were distributed in an upstream–downstream manner with contact zones localized at confluences featuring abrupt shifts from tributary to river habitat. In two drainages, the typical up and downstream positions of species were reversed. Phenotype differences between the species reflect predicted selection differences along stream gradients. Downstream populations (lower food availability and greater predator pressure) generally showed larger investment in reproduction (higher gonadal somatic index), smaller body size and lower somatic condition compared to upstream populations. Phenotypic differences between the species in the two reversed drainages were consistent with convergence of life history traits in the respective habitats. Phenotypes of individuals of hybrid origin (F1 hybrids or backcrosses) were not significantly different from the average of the two parental forms, though there were trends towards reduced fitness. The prevalence of hybridization among drainages ranged from no hybrids in two drainages to near random mating. The strongest correlates of hybridization rate among replicate hybrid zones were similarity in body shape and the homogeneity of habitat through tributary-river confluences. The two reversed orientation hybrid zones also exhibited high prevalence of hybrids suggesting that phenotypic convergence could lead to increased hybridization.

Agonistic behavioral interactions between introduced western mosquitofish and native topminnows

The stocking of western mosquitofish Gambusia affinis for mosquito control negatively impacts native fishes with similar ecological requirements. In this study, a series of laboratory microcosm experiments was used to examine intra and interspecific agonistic behavioral interactions (e.g., chases and nips) between western mosquitofish and northern starhead topminnow Fundulus dispar, northern studfish F. catenatus, blackstripe topminnow F. notatus, and banded killifish F. diaphanous at three fish densities and in the presence/absence of vegetation. Western mosquitofish exhibited more agonistic behaviors than the four topminnow species and caused a change in topminnow behavior in mixed-species microcosms. Mosquitofish were aggressive toward conspecifics, with most of the chases and nips occurring at the highest densities and when vegetation was absent. Topminnows exhibited few agonistic behaviors toward conspecifics, but intraspecific chasing and nipping did occur when exposed to mosquitofish. Agonistic behaviors by topminnows toward mosquitofish occurred infrequently, and mosquitofish initiated almost all of the chases and nips. While all four topminnow species were attacked by mosquitofish, northern starhead topminnow and banded killifish were chased and nipped more frequently than the other topminnow species. These two topminnows exhibited the most behavioral changes and fin damage and one northern starhead topminnow died following mosquitofish attacks. Based on these results, it appears that the stocking of western mosquitofish into primary and connecting waterways could have negative impacts on native topminnow species that occur in these systems.

The effects of age, sex, and habitat on body size and shape of the blackstripe topminnow,Fundulus notatus(Cyprinodontiformes: Fundulidae) (Rafinesque 1820)

Lake and stream habitats pose a variety of challenges to fishes due to differences in variables such as water velocity, habitat structure, prey community, and predator community. These differences can cause divergent selection on body size and/or shape. Here, we measured sex, age, length, and eight different morphological traits of the blackstripe topminnow, Fundulus notatus, from 19 lake and stream populations across four river drainages in central Illinois. Our goal was to determine whether size and shape differed consistently between lake and stream habitats across drainages. We also considered the effects of age and sex as they may affect size and morphology. We found large differences in body size of age 1 topminnows where stream fish were generally larger than lake fish. Body shape mainly varied as a function of sex. Adult male topminnows had larger morphological traits (with the exception of body width) than females, in particular longer dorsal and anal base lengths. Subtle effects of habitat were present. Stream fish had a longer dorsal fin base than lake fish. These phenotypic patterns may be the result of genetic and/or environmental variation. As these lakes are human-made, the observed differences, if genetic, would have had to occur relatively rapidly (within about 100 years). © 2013 The Linnean Society of London

Mercury in small Illinois fishes: historical perspectives and current issues

Documenting long-term trends in mercury deposition and/or accumulation is important in setting regulatory benchmarks, modeling contaminant transfer and flux, measuring success of environmental controls, and even assigning responsibility for pollution. We conducted a study to compare mercury concentrations in small fishes from "high-mercury" and "low-mercury" regions of Illinois, as well as to examine historic patterns of mercury availability using preserved fishes. Mercury concentrations were greater in four species of small fishes collected from a stream in a "high-mercury" region than in those same taxa collected from a stream in a "low-mercury" area in Illinois. Mercury concentrations in blackstripe topminnows (Fundulus notatus) declined dramatically between 1900 and 1961/2006 in the "high-mercury" stream, presumably due reductions in mercury releases from local and regional sources. Preserved fish had an apparent increase in mercury concentrations for up to 12months, which is consistent with changes in mass and loss of proteins observed in other studies, and we recommend that recent samples be preserved for at least 12months before comparison with older fluid-preserved material. Based on our results, further studies of mercury in small fishes in Illinois streams appear warranted.

Effects of terrestrial invertebrate reduction on three stream fishes in experimental mesocosms

Terrestrial invertebrates (TIs) provide an important trophic subsidy for many stream fishes. However, more information is needed regarding the degree to which different species rely on this subsidy and the potential consequences of altering subsidy levels. Such information is important for understanding foodweb dynamics and predicting patterns of community change as subsidy levels vary among habitats and over time. I manipulated TI inputs to experimental streams and tested for effects on diet and body condition of fishes from 3 different trophic functional groups. Study species included a TI specialist (blackstripe topminnow Fundulus notatus), a benthic invertebrate specialist (orangethroat darter Etheostoma spectabile), and an invertebrate generalist (bigeye shiner Notropis boops). Both F. notatus and N. boops changed diets under TI reduction, but only F. notatus body condition decreased, probably because of its lesser ability to use autochthonous resources. Notropis boops body condition was unchanged by TI reduction. Unlike F. notatus, N. boops was able to incorporate autochthonous C into body tissues, as indicated by muscle δ13C values. Etheostoma spectabile diet and body condition were unaffected by TI manipulation. These results suggest that stream fishes in functionally diverse assemblages are not affected equally by TI alteration, and that effects may be predictable based on trophic functional group classification. Such information is useful in predicting patterns of assemblage change with terrestrial subsidy reduction, as often occurs with anthropogenic landscape alteration.