Dean E. Fletcher

MOLECULAR GENETIC DISSECTION OF SPAWNING, PARENTAGE, AND REPRODUCTIVE TACTICS IN A POPULATION OF REDBREAST SUNFISH, LEPOMIS AURITUS

Despite a great diversity of reproductive behaviors in fishes, few studies have examined the genetic consequences of alternative reproductive tactics. Here we develop and employ microsatellite markers to assess genetic paternity and maternity of progeny cohorts in a population of redbreast sunfish (Lepomis auritus), a species in which males build and tend nests. Nearly 1000 progeny from 25 nests, plus nest‐attendant males and nearby adults, were genotyped at microsatellite loci that displayed more than 18 alleles each. The genetic data demonstrate that multiple females (at least two to six) spawned in each nest, their offspring were spatially dispersed across a nest, and more than 90% of the young were sired by the attendant male. However, about 40% of the nests also showed genetic evidence of low‐level reproductive parasitism, and two nests were tended by males that had fathered none of the sampled offspring. Genetically deduced reproductive behaviors in this population of redbreast sunfish contrast with those reported previously in bluegill sunfish (L. macrochirus) wherein heteromorphic males specialized for parasitism or for parental care coexist in high frequency. Thus, nest‐parasitic reproductive behaviors in fishes appear to be evolutionary labile.

Genetic monogamy and biparental care in an externally fertilizing fish, the largemouth bass (Micropterus salmoides).

Breeding, male North American sunfish (Centrarchidae), are often brightly coloured and promiscuous. However, the largemouth bass (Micropterus salmoides) is sexually monomorphic in appearance and socially monogamous. Unlike some other nest–tending centrarchids in the genus Lepomis, largemouth bass have also been reported to provide biparental care to eggs and fry. Here we use microsatellite markers in order to test whether social monogamy predicts genetic monogamy in the largemouth bass. Offspring were collected from 26 nests each usually guarded by a pair of adults, many of which were also captured. Twenty–three of these progeny cohorts (88%) proved to be composed almost exclusively of full–sibs and were thus the product of monogamous matings. Cuckoldry by males was rare. The genetic data also revealed that some nests contain juveniles that were not the progeny of the guardian female, a finding that can be thought of as low–level ‘female cuckoldry’. Overall, however, the data provide what may be the first genetic documentation of near–monogamy and biparental care in a vertebrate with external fertilization.

Genetic documentation of filial cannibalism in nature

Cannibalism is widespread in natural populations of fishes, where the stomachs of adults frequently contain conspecific juveniles. Furthermore, field observations suggest that guardian males routinely eat offspring from their own nests. However, recent genetic paternity analyses have shown that fish nests often contain embryos not sired by the nest-tending male (because of cuckoldry events, egg thievery, or nest piracy). Such findings, coupled with the fact that several fish species have known capabilities for distinguishing kin from nonkin, raise the possibility that cannibalism by guardian males is directed primarily or exclusively toward unrelated embryos in their nests. Here, we test this hypothesis by collecting freshly cannibalized embryos from the stomachs of several nest-tending darter and sunfish males in nature and determining their genetic parentage by using polymorphic microsatellite markers. Our molecular results clearly indicate that guardian males do indeed consume their own genetic offspring, even when unrelated (foster) embryos are present within the nest. These data provide genetic documentation of filial cannibalism in nature. Furthermore, they suggest that the phenomenon may result, at least in part, from an inability of guardians to differentiate between kin and nonkin within their own nests.

Parentage and Nest Guarding in the Tessellated Darter (Etheostoma olmstedi) Assayed by Microsatellite Markers (Perciformes: Percidae)

Abstract Parental investment as manifested through extended parental care of young presumably enhances the reproductive success of the custodial parent. In the Tessellated Darter (Etheostoma olmstedi), the primary caregivers are breeding males on the nest. However, prior field observations on nesting darters seem suggestive of behaviors that are more difficult to interpret evolutionarily. These include tending clutches that may have been fertilized by other males and appropriating nests from smaller courting males. To address such possibilities genetically, we assayed six microsatellite loci in 16 nest-tending males and the embryos from their associated clutches. In most cases, a guardian male had sired nearly all of the embryos in his nest. However, in one nest, a guardian male had been cuckolded, and in two other nests, an attendant male guarded embryos that were not his own presumably resulting from nest takeovers. From direct genotypic counts, a mean of at least 3.2 mothers contributed to the progeny in a nest, and computer simulations suggest that the true maternal number may be substantially higher.

Nest association of dusky shiners (Notropis cummingsae) and redbreast sunfish (Lepomis auritus), a potentially parasitic relationship

Age-specific habitat segregation and localized migrations to spawning grounds were noted in Notropis cummingsae (dusky shiner) in the Savannah River drainage, South Carolina. Notropis cummingsae spent most of their adult lives associated with noticeable current, usually in scour pools or eddies. Slow, still pools were used for spawning and larval rearing. The young N. cummingsae remained in the pools until juveniles, then joined the adults in faster water. Within pools, N. cummingsae spawned in the nests of Lepomis auritus (redbreast sunfish). The L. auritus defended their nests from N. cummingsae, but the symbionts accessed the nest primarily when the guarding male host was away from the nest or preoccupied with another centrarchid. While on the spawning grounds, N. cummingsae fed voraciously on eggs within the centrarchid nests. Gut content analysis of these N. cummingsae indicated that they ate almost exclusively centrarchid eggs/larvae even though eggs/larvae of both species were in the nest. A mean of up to 9.2 larvae was eaten per N. cummingsae, and from 15 to over 100 individuals were observed in a nest at one time. Predation of eggs/larvae by N. cummingsae appears to reduce the reproductive success of the host, resulting in a parasitic nest association, but more detailed research is necessary to determine this unequivocally.

The genetic mating system of spotted sunfish (Lepomis punctatus): mate numbers and the influence of male reproductive parasites.

In nest‐building fish species, mature males often exhibit one of two alternative reproductive behaviours. Bourgeois males build nests, court females, and guard their eggs. Parasitic cuckolders attempt to steal fertilizations from bourgeois males and do not invest in parental care. Previous evidence from the bluegill sunfish (Lepomis macrochirus) suggests that adult males are morphologically specialized for these two tactics. Here, we used microsatellite markers to determine genetic parentage in a natural population of the spotted sunfish (L. punctatus) that also displayed both bourgeois and parasitic male morphs. As gauged by relative investments in gonadal vs. somatic tissues, between 5 and 15% of the mature adult males were parasites. Multi‐locus genotypes were generated for more than 1400 embryos in 30 nests, their nest‐guardian males, and for other adults in the population. Progeny in approximately 57% of the nests were sired exclusively by the guardian male, but the remaining nests contained embryos resulting from cuckoldry as well. Overall, the frequency of offspring resulting from stolen fertilizations was only 1.3%, indicating that the great majority of paternity is by bourgeois nesting males. With regard to maternity, 87% of the nests had at least three dams, and computer simulations estimate that about 7.2 dams spawned per nest.

Influence of riparian alteration on canopy coverage and macrophyte abundance in Southeastern USA blackwater streams

Abstract Two tributary streams (Fourmile branch and Pen branch) located on the US Department of Energys Savannah river site in west-central South Carolina, USA received thermal discharges from nuclear production reactors for over 30 years. Effluent releases produced stream water temperatures of over 50°C and stream flows of ten times above their base level. Consequently, existing plant and animal communities within the stream channels were killed and riparian zones largely destroyed. We compared canopy coverage and macrophyte abundance in these disturbed streams after 7–13 years of ambient flows and compared them to two similar, undisturbed streams. We also examined the effects of a more recent woody canopy removal associated with a restoration effort in ‘treated’ sections of Pen branch. We collected data in Spring and Fall from May 1995 through May 1997. A gradient in canopy cover existed, ranging from a fully open herbaceous canopy in the treated sections of Pen branch, through a moderately closed canopy of herbaceous plants, shrubs, and willows in the post-thermal ‘control’ streams, to a nearly closed hardwood tree canopy in the undisturbed streams. Even though Fourmile branch had 3 more years of growth, Pen branch had a more closed upper canopy. Total aquatic macrophyte abundance was negatively related to canopy cover producing nearly the reverse gradient among streams as did the canopy cover. However, control sections of Pen branch had a more closed canopy than Fourmile branch, but total macrophyte abundance was higher in Pen branch. This can be attributed to the presence of submergent macrophytes in Pen branch that were absent in Fourmile branch. Different structural types of macrophytes varied in their degree of limitation by canopy coverage and in their seasonal patterns of growth. Stream habitats remain severely altered due to destruction of the riparian vegetation by past thermal effluents. The full range of effects of the alteration of canopy coverage and the resultant macrophyte abundances on these streams should be the focus of future analyses.

Geckos as indicators of mining pollution

Catastrophic collapse of a mine tailings dam released several million cubic meters of toxic mud and acidic water into the Guadiamar River valley, southern Spain, in 1998. Remediation efforts removed most of the sludge from the floodplain, but contamination persists. Clean-up activities also produced clouds of aerosolized materials that further contaminated the surrounding landscape. Whole-body concentrations of 21 elements in the Moorish wall gecko, Tarentola mauritanica, a common inhabitant of both rural and urban areas, were compared among seven locations. Locations spanned an expected contamination gradient and included a rural and an urban non-mine-affected location, two mine-affected towns, and three locations on the contaminated floodplain. Multivariate analyses of whole-body concentrations identified pollutants that increased across the expected contamination gradient, a trend particularly evident for As, Pb, and Cd. Additionally, higher contaminant concentrations occurred in prey items eaten by geckos from mine-affected areas. Comparison of element concentrations in tails and whole bodies suggests that tail clips are a viable nondestructive index of contaminant accumulation. Our results indicate that areas polluted by the mine continue to experience contamination of the terrestrial food chain. Where abundant, geckos represent useful taxa to study the bioavailability of some hazardous pollutants.

Spawning Behavior and Genetic Parentage in the Pirate Perch (Aphredoderus sayanus), a Fish with an Enigmatic Reproductive Morphology

Abstract We describe for the first time reproductive behaviors in the Pirate Perch (Aphredoderus sayanus), a secretive nocturnal fish whose urogenital opening is positioned far anteriorally, under its throat. Some naturalists had speculated that this peculiar morphological condition might serve to promote egg transfer to the fishs branchial chamber for gill-brooding; others hypothesized that Pirate Perch spawn in the substrate of streams but offered no adaptive rationale for the odd placement of the fishs urogenital pore. Here we solve the conundrum through a combination of intensive field investigations, underwater filming, and molecular parentage analyses. We show that Pirate Perch spawn in underwater root masses, the first documentation of such nesting behavior in any species of North American fish. Female Pirate Perch thrust their heads and release their eggs into sheltered canals of these masses. Males congregate at these sites and likewise enter the narrow canals headfirst, to release sperm. Thus, the forward-shifted urogenital pore may facilitate spawning under this special nesting circumstance. We found no evidence of extended parental care. Fish formed their own canals or used burrows made by aquatic macro-invertebrates and salamanders. Genetic analyses based on three polymorphic microsatellite loci demonstrate that a total of at least five to 11 sires and dams were the parents of embryos within each of three assayed root-mass nests (of a total of 23 nests found). Males defended the oviposition sites by body-plugging canal entrances after spawning. This and more direct aggressive behaviors by males probably relate to selection pressures imposed by intense competition for fertilization success under these group-spawning conditions.

Effects of disturbance at two spatial scales on macroinvertebrate and fish metrics of stream health

We analyzed macroinvertebrate and fish assemblage data collected from the upper southeastern coastal plain of the USA to (1) assess the relative sensitivities of bioassessment metrics to in-stream habitat quality, catchment scale land disturbance, and the presence of a reservoir in the catchment and (2) determine whether fish differ from macroinvertebrates in their responses to these variables. Fish and macroinvertebrates responded differently to anthropogenic disturbance: macroinvertebrates were affected most strongly by in-stream habitat quality and fish by the presence of a reservoir in the catchment. Neither taxonomic group were significantly affected by the catchment scale disturbance, probably because the proportions of disturbed land in the study areas were low. Fish may be particularly sensitive to the presence of reservoirs because of their need to cover relatively large distances to complete life cycles and maintain viable populations and because of their sensitivity to the effects of invasive reservoir species, particularly predator fishes. Although not an important predictor in itself, disturbance at the watershed scale was significantly and positively related to in-stream habitat quality, indicating that watershed disturbance had an important indirect effect on aquatic organisms. Direct and indirect ordination showed that the metric data were more strongly related to the disturbance variables than the taxonomic data from which the metrics were derived, possibly because the metrics were less sensitive than the taxon-specific abundances to nondisturbance-related factors. Other factors that may have contributed to this result include greater statistical tractability of the metric data and the relatively high sensitivity of the collective properties represented by the metrics to disturbance-related environmental changes.