Sunfishes (Centrarchidae)

Native to North America, sunfishes in the family Centrarchidae are an abundant and conspicuous element of the continent’s ichthyofauna. This chapter describes genetic research on topics ranging from intraspecific geographic variation in bluegills to the evolutionary consequences of introgression in hybrid-swarming basses, to speciational histories of this endemic taxonomic group, to genetic assessments of paternity and maternity in several of these nest-tending species.

Keywords

Lepomis; Micropterus; genetic parentage; hybridization; introgression; protein electrophoresis; microsatellite loci; phylogenetics; speciation; phyletic gradualism; punctuated equilibrium; heterozygosity; population structure; hybrid swarm

Introduction

JCA’s baccalaureate degree (from the University of Michigan’s School of Natural Resources in 1970) was in Fisheries Biology and Management. Thus, it should come as no surprise that much of his subsequent research in molecular ecology and evolution over the ensuing decades has been on fishes. His Master’s degree (from the University of Texas in 1971) involved an examination of genetic variability in Mexican cavefishes (see Chapter 4), and his dissertation work for Ph.D. (from the University of California at Davis in 1975) entailed a comparison of molecular evolutionary rates in rapidly speciating minnows (Cyprinidae) versus slower speciating sunfishes (Centrarchidae). The North American sunfishes have long been of special research interest in the JCA laboratory, because of their diverse nature (with about 25 species), their usual abundance in native waterways, their interesting ecologies that include nest-building habits and large clutches that almost beg for molecular appraisals of genetic parentage, and their natural proclivity to hybridize both in natural and contrived settings. The abstracts in this chapter reflect JCA’s longstanding fascination with sunfishes, some of his favorite creatures. Several of the earliest papers in this series were conducted while JCA was a laboratory technician at the Savannah River Ecology Laboratory in South Carolina, from 1971 to 1973. But his special interest in the beautiful centrarchid species has persisted to the present day.

Biochemical genetics of sunfish I. Geographic variation and subspecific intergradation in the bluegill, Lepomis macrochirus

Avise, J.C. and M.H. Smith. 1974. Biochemical genetics of sunfish I. Geographic variation and subspecific intergradation in the bluegill, Lepomis macrochirus. Evolution 28:42–56.

Anecdote or Backdrop

The bluegill sunfish is probably the most abundant and widespread freshwater fish native to the eastern United States, being found in bodies of water ranging from small rivers to huge reservoirs. Because it is so common, it proved to be a suitable candidate for one of the first range-wide genetic surveys of any fish species in the protein-electrophoretic era. On one extended road trip in February 1972, we collected this species from the Carolinas to Texas, sometimes seining the fish from icy waters that required our use of wetsuits.

Abstract

Electrophoretic variation in proteins encoded by 15 genetic loci was analyzed in 2415 bluegill (Lepomis macrochirus) representing 47 populations from 7 southern states. Populations from the Florida peninsula and southeastern Georgia (L.m. purpurescens) differ in allelic composition at several loci from populations in central and western Georgia west to Texas (L.m. macrochirus), yielding coefficients of genetic similarity below the range typifying continuously distributed conspecific populations in other vertebrates, but quite comparable to previous reports for various semispecies pairs. Within several river drainages in South Carolina and Georgia, bluegill populations are segregating for alleles from both subspecies. A closer examination of genotypic classes in a large population from the intergrade zone confirms that the two subspecies are backcrossing and are apparently fully interfertile. The high correlation of allele frequencies across locales in the hybrid zone is compatible with the hypothesis that the alleles are behaving as neutral markers of intergradation. The pattern of introgression evidences a secondary meeting of allopatrically evolved races. Since populations of L.m. purpurescens are largely confined to the Florida peninsula, it is likely that Pleistocene rises in sea level were important in their original isolation from L.m. macrochirus. Populations of bluegill within reservoirs are generally homogeneous for frequencies of common alleles at polymorphic loci, but there is significant heterogeneity in allele frequencies between reservoirs within a drainage. The magnitude of this variance is greatest in the intergrade populations of the Savannah River basin and is far less in populations of L.m. macrochirus. The bluegill examined may be characterized by three areas of relative genetic uniformity: Florida populations of L.m. purpurescens, intergrade populations, and populations of L.m. macrochirus to the west.

Addendum

The bluegill is a popular “panfish” that is widely bred commercially and used to stock farm ponds. For this reason, we confined our collecting to more natural or open habitats that probably had not been recently stocked with captive-bred specimens. This means that most of the fish surveyed in this study were captured from rivers or large open-water reservoirs, where reproduction presumably occurs naturally rather than in fish hatcheries.

Biochemical genetics of sunfish II. Genic similarity between hybridizing species

Avise, J.C. and M.H. Smith. 1974. Biochemical genetics of sunfish II. Genic similarity between hybridizing species. American Naturalist 108:458–472.

Anecdote or Backdrop

This study was conducted at a time when there was great interest but little empirical information about the magnitude of genetic divergence between closely related animal species. Early allozyme studies with fruit flies had shown that even sister species might differ in allelic composition at 20% or more of their structural loci, but would such observations extend to other taxa as well? Here we examined genetic divergence among nearly a dozen sunfish species that were presumed to be close evolutionary relatives, based on their well-known propensity to produce interspecific hybrid offspring.

Abstract

Electrophoretic variation in proteins encoded by 18 genetic loci was examined in 1099 specimens of 10 species of sunfish (Lepomis), a group renowned for its ability to hybridize both in the laboratory and in nature. Populations belonging to the same species show very little genic differentiation over considerable geographic ranges. Species pairs showed major differences in allelic composition at an average of about one-half of their loci, although the range is considerable. Thus, despite their ability to hybridize to the F1 generation, Lepomis species have very different gene pools. This indicates that close genic similarity is not a necessary corollary of hybridizing propensity in these fishes.

Addendum

It is now known that different vertebrate groups lose their capacity to produce viable hybrids at very different evolutionary rates, and that some vertebrates may retain this capacity for more than 10 million years.

Biochemical genetics of sunfish IV. Relationships of centrarchid genera

Avise, J.C., D.O. Straney, and M.H. Smith. 1977. Biochemical genetics of sunfish IV. Relationships of centrarchid genera. Copeia 1977:250–258.

Anecdote or Backdrop

By the mid 1970s, it was becoming evident that multi-locus protein-electrophoretic data contained at least some useful evolutionary information about conspecific populations and congeneric taxa. What remained unknown, however, was whether any such phylogenetic insights might be gleaned from allozymic comparisons among more distantly related taxa, such as species belonging to confamilial genera. This paper was one of our earliest attempts to address this issue.

Abstract

We examined electrophoretic variation in proteins encoded by 11–14 loci in species representing all 9 genera of Centrarchidae. A dendrogram based on allozyme information is compared to postulated relationships of sunfish genera based on general and specific morphologies, and on hybridizing propensity. The allozyme information correlates most strongly with that derived from a detailed study of the acoustico-lateralis system by Branson and Moore. Similarities between the two sets of data are observed (i) in the clustering together of species of Lepomis, (ii) in the clustering of Lepomis with Micropterus, (iii) in the placement of Acantharchus with Archoplites, and (iv) in the very distant relationship of Elassoma to the other centrarchid genera. Levels of genetic similarity (S) between centrarchid genera are compared to previously published levels of similarity between congeneric species of Lepomis, subspecies of Lepomis macrochirus, and geographic populations within the subspecies L.m. macrochirus and L.m. purpurescens. Mean values of S are as follows: between genera, S=0.29; between...