Faculty Seed Grant Projects

Spatio-temporal dynamics of fish reproductive mutualisms and linkages to the spread of invasives


Biological invasions are leading causes of global change and biodiversity decline. Critical to mitigating ongoing invasions and limiting anthropogenic actions that encourage introduction of non-natives is an understanding of mechanisms that facilitate invader success. Certain biological traits that are essentially the opposites of traits that promote species rarity and imperilment are emerging as attributes of invasiveness. For many animal taxa, fecundity, mobility, and complex modes of reproduction (e.g., egg burying, nesting, and defense of eggs/larvae in fishes) that enhance survival of offspring, have been linked to population dynamics as expressed in high local density and large range size, and consequently to invasion success. Another process, much less understood, is how biotic interactions (e.g., mutualisms) facilitate establishment and spread of introduced species.

The New River basin (NR) is a natural laboratory for fish invasions but no systematic study of invasions occurred there until recently, led by our multidisciplinary team. Of ~80 fish species established in the basin, 40 (50%) were introduced over the last two centuries. Collection records from the last 70 years have shown rapid range expansion of at least 33% of all fishes in the basin, with nest-building cyprinids and their associates (mutualists) among the most rapid invaders. For example, Bluehead Chub (Nocomis leptocephalus)– mound-builder, Central Stoneroller (Campostoma anomalum)– pit-builder, and Creek Chub (Semotilus atromaculatus)– pit-ridge builder occur syntopically in Toms Creek (TC), a tributary of the NR, along with 8-9 other cyprinids, the majority of which associate with these nest builders during the reproductive season. Central Stoneroller is both a nest-builder and an associate of other nest-builders, forming a complex context-dependent mutualism that remains poorly understood. The nest-builders are native to the NR but 10 of 20 cyprinids designated as introduced or possibly introduced (e.g., Crescent Shiner Luxilus cerasinus and Highback Chub Hybopsis hypsinotus), and common in the NR and neighboring basins, also exhibit nest-associative reproductive behaviors. Contrary to theoretical predictions, these introduced reproductive mutualists could be successful invaders because 1) most are facultative, and 2) the nest-host genera (with multiple ecologically similar species) are widely distributed in the NR basin and throughout eastern North America.

Bluehead chub (Nocomis leptocephalus) near a nesting mound

In a broader scale analysis throughout the NR, nester and associate range expansions have occurred concomitantly with the decline in the range of other species (e.g., Rosyface Shiner Notropis rubellus, Silver Shiner N. photogenis, Tonguetied Minnow Exoglossum laurae, and Sharpnose Darter Percina oxyrhynchus). Within TC, the range of S. atromaculatus has expanded several kilometers downstream since 2008, while N. rubellus appears to have become rarer in TC. This, in part, portrays the so called ‘native invasions’ process, with the potential to competitively displace other natives and drive them toward imperilment. Such displacements also occur in other basins. Recently, we have leveraged NSF funding and used DNA barcoding of eggs and larvae from nests, in conjunction with underwater HD videography and community sampling, to determine the extent of reproductive interactions among the cyprinids in TC.

Three objectives will be addressed:

  1. Determine the longitudinal (upstream-downstream) and temporal (throughout spawning season) variation in egg composition from pit, pit-ridge, and mound nests in TC
  2. Determine the extent and direction of movement by nest-building males during the spawning season
  3. Estimate the age 1+ species composition of all cyprinids before, during, and at the end of spawning and relate species composition to egg composition.

Field methods are in addition to analysis of literature and agency data. Toms Creek will be divided into five 2-km sections, with a 0.5-km study reach established in each section. In March, prior to spawning season, backpack electrofishing will be conducted to i) estimate species composition and ii) mark and release adult males of Bluehead Chub, Creek Chub, and Central Stoneroller. Marking will be done with the fluorescent visible implant elastomers (VIE) using colors and mark locations to uniquely identify fish from each section. Adults will be re-sampled two weeks after marking and at the end of June to determine community composition, adult population abundances, and final locations of marked individuals, which will provide a semi-quantitative measure of movement extent. During the spawning season, sites will be visited daily for underwater video observations and weekly for egg sampling. Eggs will be chilled immediately after collection and DNA will be extracted within three days on 30-40 eggs.

The longitudinal stream gradient provides a wide range of species richness and interactions, mimicking interactions across entire basins. This provides a cost-effective, intensive study that forms the basis for a larger proposal intended to cover the New River and neighboring basins.