Molecular and morphological evidence for hybridization between two ecologically distinct grasshoppers (Melanoplus sanguinipes and M. devastator) in California

Abstract

This paper applies the biological species concept to two ecologically distinct species of grasshopper, Melanoplus sanguinipes and M. devastator, by testing for reproductive isolation in the field in California. Two independent techniques for assessing gene flow between species were employed. Firstly, we examined male genitalic morphology in populations from the foothills of the Sierra Nevada where the two species are parapatric. Two genetically based genitalic traits that differed between allopatric populations of each species formed a dine in this zone. Males captured in the field from the region of parapatry resembled offspring from interspecific laboratory hybridizations. Secondly, we surveyed electrophoretic variation of populations from across California and used F statistics to estimate levels of gene flow within and between species. Results from both morphology and F statistics suggested that these grasshoppers are not reproductively isolated in nature hut that gene flow between species is reduced relative to within-species. These field results were consistent with a laboratory study that showed partial hut not complete hybrid egg inviability. Because the hybrid zone is centred along an ecological transition, this system offers an opportunity to investigate whether adaptive changes across the zone contribute to reduced gene flow between species.

Altitudinal variation for senescence in Melanoplus grasshoppers

“…For instance, within D. melanogaster, genetic studies of the relationship between body size and longevity have failed to establish an association of these traits (Hillesheim and Stearns 1991;Partridge et al 1995;Zwaan et al 1995b). In M. sanguinipes/devastator of the Sierra Nevada, high-elevation populations are smaller than low-elevation populations in both the ®eld and when individuals are reared under common laboratory conditions (here, and Orr et al 1994). Thus, among populations mean body size and longevity are correlated, but it is unlikely that variation in body size produces our observed cline for senescence.…”

“…In the Sierra Nevada, M. sanguinipes occurs at middle and high elevation while M. devastator occurs in the lower foothills and into the sea level Central Valley (Gurney and Brooks 1959;Strohecker et al 1968). A zone of hybridization occurs between M. devastator and M. sanguinipes in the Sierra Nevada centered at 700 m (Orr et al 1994). Orr et al (1994) found extensive introgression between the nominal taxa across this zone, and phenograms based on electrophoretic data show that M. devastator populations are nested completely within those of M. sanguinipes.…”

“…A zone of hybridization occurs between M. devastator and M. sanguinipes in the Sierra Nevada centered at 700 m (Orr et al 1994). Orr et al (1994) found extensive introgression between the nominal taxa across this zone, and phenograms based on electrophoretic data show that M. devastator populations are nested completely within those of M. sanguinipes. Since genē ow of bene®cial alleles can be signi®cant across hybrid zones where genetic distance between nominal species is small (Barton and Bengtsson 1986;Barton and Hewitt 1989), Orr et al (1994) suggested that we treat this complex as a continuous genetic population that is structured primarily by distance and elevation.…”

Genetic Variation and Population Structure of Oriental Migratory Locust, Locusta migratoria manilensis, in China by Allozyme, SSRP-PCR, and AFLP Markers

“…In our study, the eight L. m. manilensis populations show an overall heterozygote deficiency, which results in significant Hardy-Weinberg disequilibrium. This deviation has also been observed in other Orthoptera species (Allegrucci et al, 1997;Orr et al, 1994). Heterozygote deficiency can be the consequence of several factors, including inbreeding, nonrandom mating, bottleneck effects, and parthenogenesis (Hong and Ando, 1998).…”

Combining DNA sequences and morphology in systematics: testing the validity of the dragonfly species Cordulegaster bilineata

“…Techniques such as allozymes (Orr et al, 1994), RAPD-PCR (Wilkerson et al, 1995), RFLPs (Taylor and Szalanski, 1999) and DNA sequencing (Morrow et al, 2000) have all allowed researchers to look beyond morphological similarities and search for genetic differences that may help to solve taxonomic questions. Unfortunately, tension between molecular and morphological researchers has made studies that combine morphology and molecular analysis uncommon (eg, Orr et al, 1994;Navajas et al, 1997;Brust et al, 1998;Manguin et al, 1999;Raahauge and Kristensen, 2000).…”