Biomedical subjects

Jeffrey L Feder

Publications and source records attributed to Jeffrey L Feder.

14 recordsLinked to original sources

PubMed2006

Speciation genetics: evolving approaches.

Much progress has been made in the past two decades in understanding Darwin's mystery of the origins of species. Applying genomic techniques to the analysis of laboratory crosses and natural populations has helped to determine the genetic basis of barriers to gene flow which create new species. Although new methodologies have not changed the prevailing hypotheses about how species form, they have accelerated the pace of data collection. By facilitating the compilation of case studies, advances in genetic techniques will help to provide answers to the next generation of questions concerning the relative frequency and importance of different processes that cause speciation.

Animals↗

PubMed2006

Integrating biogeographic and genetic approaches to investigate the history of bioluminescent colour alleles in the Jamaican click beetle, Pyrophorus plagiophthalamus.

Bioluminescent colour in the Jamaican click beetle, Pyrophorus plagiophthalamus, is an ideal system for studies moving from gene to landscape to gain a holistic understanding of the molecular, ecological, and historical bases for adaptation. Previous studies have established the genetics of bioluminescent colour variation in the beetle to the level of the nucleotide base pair in the target gene luciferase. Three different luciferase colour alleles affecting ventral light organ colour [yellow-green (vYG), yellow (vYE), and orange (vOR)] were found segregating in P. plagiophthalamus populations. These alleles differ from each other in a number of replacement mutations (14 total), the majority of which (11) have a measurable effect on colour. Phylogenetic analysis revealed a long-term adaptive trend on Jamaica towards longer wavelength bioluminescence, culminating in the most recently derived vOR allele. Here, we further investigate the historical and geographic context of adaptive colour evolution by testing a vicariance model for the origins of the extant ventral light organ polymorphism: that the vOR allele arose and differentiated in an isolated deme on the east side of Jamaica before spreading westward. Comparisons of colour phenotypes, luciferase coding sequences, the third intron of the gene, mtDNA, and microsatellite data provided evidence for past population subdivision on Jamaica and ongoing gene flow, as has been found for other island endemics. However, the pattern of differentiation supported the allopatric divergence of vYG and vYE alleles. The vOR gene appears to have arisen relatively recently from a vYE precursor and postdates the period of major biogeographic isolation. We discuss the implications of the results for discerning ecological causation in the adaptive sequence from nucleotide to landscape to population change for bioluminescent colour.

Adaptation, Physiological↗

PubMed2006

Receptor expression and sympatric speciation: unique olfactory receptor neuron responses in F1 hybrid Rhagoletis populations.

The Rhagoletis pomonella species complex is one of the foremost examples supporting the occurrence of sympatric speciation. A recent study found that reciprocal F(1) hybrid offspring from different host plant-infesting populations in the complex displayed significantly reduced olfactory host preference in flight-tunnel assays. Behavioral and electrophysiological studies indicate that olfactory cues from host fruit are important chemosensory signals for flies to locate fruit for mating and oviposition. The reduced olfactory abilities of hybrids could therefore constitute a significant post-mating barrier to gene flow among fly populations. The present study investigated the source of changes in the hybrid olfactory system by examining peripheral chemoreception in F(1) hybrid flies, using behaviorally relevant volatiles from the parent host fruit. Single-sensillum electrophysiological analyses revealed significant changes in olfactory receptor neuron (ORN) response specificities in hybrid flies when compared to parent ORN responses. We report that flies from F(1) crosses of apple-, hawthorn- and flowering dogwood-origin populations of R. pomonella exhibited distinct ORN response profiles absent from any parent population. These peripheral alterations in ORN response profiles could result from misexpression of multiple receptors in hybrid neurons as a function of genomic incompatibilities in receptor-gene pathways in parent populations. We conclude that these changes in peripheral chemoreception could impact olfactory host preference and contribute directly to reproductive isolation in the Rhagoletis complex, or could be genetically coupled to other host-associated traits.

Animals↗

PubMed2005

Mayr, Dobzhansky, and Bush and the complexities of sympatric speciation in Rhagoletis.

The Rhagoletis pomonella sibling species complex is a model for sympatric speciation by means of host plant shifting. However, genetic variation aiding the sympatric radiation of the group in the United States may have geographic roots. Inversions on chromosomes 1-3 affecting diapause traits adapting flies to differences in host fruiting phenology appear to exist in the United States because of a series of secondary introgression events from Mexico. Here, we investigate whether these inverted regions of the genome may have subsequently evolved to become more recalcitrant to introgression relative to collinear regions, consistent with new models for chromosomal speciation. As predicted by the models, gene trees for six nuclear loci mapping to chromosomes other than 1-3 tended to have shallower node depths separating Mexican and U.S. haplotypes relative to an outgroup sequence than nine genes residing on chromosomes 1-3. We discuss the implications of secondary contact and differential introgression with respect to sympatric host race formation and speciation in Rhagoletis, reconciling some of the seemingly dichotomous views of Mayr, Dobzhansky, and Bush concerning modes of divergence.

Animals↗

PubMed2005

Habitat avoidance: overlooking an important aspect of host-specific mating and sympatric speciation?

Understanding speciation requires discerning how reproductive barriers to gene flow evolve between previously interbreeding populations. Models of sympatric speciation for phytophagous insects posit that reproductive isolation can evolve in the absence of geographic isolation as a consequence of an insect shifting and ecologically adapting to a new host plant. One important adaptation contributing to sympatric differentiation is host-specific mating. When organisms mate in preferred habitats, a system of positive assortative mating is established that facilitates sympatric divergence. Models of host fidelity generally assume that host choice is determined by the aggregate effect of alleles imparting positive preferences for different plant species. But negative effect genes for avoiding nonnatal plants may also influence host use. Previous studies have shown that apple and hawthorn-infesting races of Rhagoletis pomonella flies use volatile compounds emitted from the surface of fruit as key chemosensory cues to recognize and distinguish between their host plants. Here, we report results from field trials indicating that in addition to preferring the odor of their natal fruit, apple and hawthorn flies, and their undescribed sister species infesting flowering dogwood (Cornus florida), also avoid the odors of nonnatal fruit. We discuss the implications of nonnatal fruit avoidance for the evolutionary dynamics and genetics of sympatric speciation. Our findings reveal an underappreciated role for habitat avoidance as a potential postmating, as well as prezygotic, barrier to gene flow.

Animals↗

PubMed2005

The genetic basis for fruit odor discrimination in Rhagoletis flies and its significance for sympatric host shifts.

Rhagoletis pomonella (Diptera: Tephritidae) use volatile compounds emitted from the surface of ripening fruit as important chemosensory cues for recognizing and distinguishing among alternative host plants. Host choice is of evolutionary significance in Rhagoletis because these flies mate on or near the fruit of their respective host plants. Differences in host choice based on fruit odor discrimination therefore result in differential mate choice and prezygotic reproductive isolation, facilitating sympatric speciation in the absence of geographic isolation. We test for a genetic basis for host fruit odor discrimination through an analysis of F2 and backcross hybrids constructed between apple-, hawthorn-, and flowering dogwood-infesting Rhagoletis flies. We recovered a significant proportion (30-65%) of parental apple, hawthorn, and dogwood fly response phenotypes in F2 hybrids, despite the general failure of F1 hybrids to reach odor source spheres. Segregation patterns in F2 and backcross hybrids suggest that only a modest number of allelic differences at a few loci may underlie host fruit odor discrimination. In addition, a strong bias was observed for F2 and backcross flies to orient to the natal fruit blend of their maternal grandmother, implying the existence of cytonuclear gene interactions. We explore the implications of our findings for the evolutionary dynamics of sympatric host race formation and speciation.

Animals↗

PubMed2004

Postzygotic isolating factor in sympatric speciation in Rhagoletis flies: reduced response of hybrids to parental host-fruit odors.

Rhagoletis pomonella is a model for sympatric speciation (divergence without geographic isolation) by means of host-plant shifts. Many Rhagoletis species are known to use fruit odor as a key olfactory cue to distinguish among their respective host plants. Because Rhagoletis rendezvous on or near the unabscised fruit of their hosts to mate, behavioral preferences for fruit odor translate directly into premating reproductive isolation among flies. Here, we report that reciprocal F(1) hybrids between the apple and hawthorn host races of R. pomonella, as well as between the host races and an undescribed sibling species infesting Cornus florida (flowering dogwood) do not respond to host fruit volatiles in wind-tunnel assays at doses that elicit maximal directed flight in parental flies. The reduced ability of hybrids to orient to fruit volatiles could result from a conflict between neural pathways for preference and avoidance behaviors, and it suggests that hybrids might suffer a fitness disadvantage for finding fruit in nature. Therefore, host-specific mating may play a dual role as an important postzygotic as well as a premating reproductive barrier to isolate sympatric Rhagoletis flies.

Animals↗

PubMed2003

Darwinian natural selection for orange bioluminescent color in a Jamaican click beetle.

The Jamaican click beetle Pyrophorus plagiophthalamus (Coleoptera: Elateridae) is unique among all bioluminescent organisms in displaying a striking light color polymorphism [Biggley, W. H., Lloyd, J. E. & Seliger, H. H. (1967) J. Gen. Physiol. 50, 1681-1692]. Beetles on the island vary in the color of their ventral light organs from yellow-green to orange and their dorsal organs from green to yellow-green. The genetic basis for the color variation involves specific amino acid substitutions in the enzyme luciferase. Here, we show that dorsal and ventral light color in P. plagiophthalamus are under separate genetic control, we resolve the allelic basis for color variation, and, through analyses of luciferase sequence variation, we demonstrate that natural selection has produced a long-term adaptive trend for longer wavelength (more orange) ventral light on Jamaica. Our results constitute a novel example connecting the selective fixation of specific nucleotides in nature to their precisely determined phenotypic effects. We also present evidence suggesting that a recently derived ventral orange luciferase allele on the island has deterministically increased in frequency. Thus, the current luciferase polymorphism for P. plagiophthalamus appears to be mirroring the long-term anagenic trend on Jamaica, revealing a possible ongoing adaptive color transition in progress.

Alleles↗

PubMed2003

Fruit odor discrimination and sympatric host race formation in Rhagoletis.

Rhagoletis pomonella is a model for incipient sympatric speciation (divergence without geographic isolation) by host-plant shifts. Here, we show that historically derived apple- and ancestral hawthorn-infesting host races of the fly use fruit odor as a key olfactory cue to help distinguish between their respective plants. In flight-tunnel assays and field tests, apple and hawthorn flies preferentially oriented to, and were captured with, chemical blends of their natal fruit volatiles. Because R. pomonella rendezvous on or near the unabscised fruit of their hosts to mate, the behavioral preference for apple vs. hawthorn fruit odor translates directly into premating reproductive isolation between the fly races. We have therefore identified a key and recently evolved (<150 years) mechanism responsible for host choice in R. pomonella bearing directly on sympatric host race formation and speciation.

Animals↗

PubMed2003

Allopatric genetic origins for sympatric host-plant shifts and race formation in Rhagoletis.

Tephritid fruit flies belonging to the Rhagoletis pomonella sibling species complex are controversial because they have been proposed to diverge in sympatry (in the absence of geographic isolation) by shifting and adapting to new host plants. Here, we report evidence suggesting a surprising source of genetic variation contributing to sympatric host shifts for these flies. From DNA sequence data for three nuclear loci and mtDNA, we infer that an ancestral, hawthorn-infesting R. pomonella population became geographically subdivided into Mexican and North American isolates approximately 1.57 million years ago. Episodes of gene flow from Mexico subsequently infused the North American population with inversion polymorphism affecting key diapause traits, forming adaptive clines. Sometime later (perhaps +/-1 million years), diapause variation in the latitudinal clines appears to have aided North American flies in adapting to a variety of plants with differing fruiting times, helping to spawn several new taxa. Thus, important raw genetic material facilitating the adaptive radiation of R. pomonella originated in a different time and place than the proximate ecological host shifts triggering sympatric divergence.

Animals↗

PubMed2003

Evidence for inversion polymorphism related to sympatric host race formation in the apple maggot fly, Rhagoletis pomonella.

Evidence suggests that the apple maggot, Rhagoletis pomonella (Diptera: Tephritidae) is undergoing sympatric speciation (i.e., divergence without geographic isolation) in the process of shifting and adapting to a new host plant. Prior to the introduction of cultivated apples (Malus pumila) in North America, R. pomonella infested the fruit of native hawthorns (Crataegus spp.). However, sometime in the mid-1800s the fly formed a sympatric race on apple. The recently derived apple-infesting race shows consistent allele frequency differences from the hawthorn host race for six allozyme loci mapping to three different chromosomes. Alleles at all six of these allozymes correlate with the timing of adult eclosion, an event dependent on the duration of the overwintering pupal diapause. This timing difference differentially adapts the univoltine fly races to an approximately 3- to 4-week difference in the peak fruiting times of apple and hawthorn trees, partially reproductively isolating the host races. Here, we report finding substantial gametic disequilibrium among allozyme and complementary DNA (cDNA) markers encompassing the three chromosomal regions differentiating apple and hawthorn flies. The regions of disequilibrium extend well beyond the previously characterized six allozyme loci, covering substantial portions of chromosomes 1, 2, and 3 (haploid n = 6 in R. pomonella). Moreover, significant recombination heterogeneity and variation in gene order were observed among single-pair crosses for each of the three genomic regions, implying the existence of inversion polymorphism. We therefore have evidence that genes affecting diapause traits involved in host race formation reside within large complexes of rearranged genes. We explore whether these genomic regions (inversions) constitute coadapted gene complexes and discuss the implications of our findings for sympatric speciation in Rhagoletis.

Adaptation, Physiological↗

PubMed2002

Importance of hybridization between indigenous and nonindigenous freshwater species: an overlooked threat to North American biodiversity.

Biodiversity of North American freshwaters is among the greatest in the world. However, due to extensive habitat degradation, pollution, and introductions of nonindigenous species, this biodiversity is also among the most endangered. Unlike habitat degradation and pollution, nonindigenous species represent a permanent loss of biodiversity because their removal or control is often impossible. Most species introduced into nonnative North American ranges, however, are not from Eurasia but have been introduced from geographically isolated regions within North America. Although the ecological effects of introduced species have been widely documented, the effects of hybridization, especially between closely related species, represents an equally serious mechanism of extinction but is much less studied. Identification of which species are likely to hybridize after contact is of critical importance to prevent the further loss of native species. Molecular phylogenetics serves as a powerful tool to identify freshwater species at risk of introgression, if we can assume that genetic distance is a good predictor of the potential for hybridization. Although not a thorough review of all cases of hybridization, this article documents the extent and effects of hybridization in fishes, crayfishes, mussels, and other invertebrates in light of the currently accepted phylogenetic relationships. We suggest this approach may be the first step in addressing the potential threat of hybridization between many of the closely related species in North American fresh waters.

Animals↗

PubMed2002

Sympatric speciation in phytophagous insects: moving beyond controversy?

Sympatric speciation is the splitting of one evolutionary lineage into two without the occurrence of geographic isolation. The concept has been intimately tied to entomology since the 1860s, when Benjamin Walsh proposed that many host-specific phytophagous insects originate by shifting and adapting to new host plant species. If true, sympatric speciation would have tremendous implications for our understanding of species and their origins, biodiversity (25-40% of all animals are thought to be phytophagous specialists), insect-plant coevolution, community ecology, phylogenetics, and systematics, as well as practical significance for the management of insect pests. During much of the twentieth century sympatric speciation was viewed as much less plausible than geographic (allopatric) speciation. However, empirical field studies, laboratory experiments, developments in population genetics theory, and phylogenetic and biogeographic data have all recently combined to shed a more favorable light on the process. We review the evidence for sympatric speciation via host shifting for phytophagous insects and propose a set of testable predictions for distinguishing geographic mode (allopatric versus sympatric) of divergence. Our conclusion is that sympatric speciation is a viable hypothesis. We highlight areas where more thorough testing is needed to move sympatric speciation into the realm of accepted scientific theory.

Animals↗

PubMed2002

Herbivorous insects: model systems for the comparative study of speciation ecology.

Does ecological divergence drive species-level evolutionary diversification? How so and to what degree? These questions were central to the thinking of the evolutionary synthesis. Only recently, however, has the ecology of speciation become an important focus of empirical study. Here, we argue that ecologically specialized, phylogenetically diverse, and experimentally tractable herbivorous insect taxa offer great opportunities to study the myriad mechanisms by which ecology may cause reproductive isolation and promote speciation. We call for the development and integrated experimental study of a taxonomic diversity of herbivore model systems and discuss the availability and recent evaluation of suitable taxa. Most importantly, we describe a general comparative framework that can be used to rigorously test a variety of hypotheses about the relative contributions and the macroevolutionary generality of particular mechanisms. Finally, we illustrate important issues for the experimental analysis of speciation ecology by demonstrating the consequences of specialized host associations for ecological divergence and premating isolation in Neochlamisus bebbianae leaf beetles.

Animals↗