Comparative Biochemical Genetics of Three Fire Ant Species in North America, with Special Reference to the Two Social Forms of Solenopsis invicta (Hymenoptera: Formicidae)

Abstract

An electrophoretic study of the genetics of three fire ant species in North America was undertaken with the primary objective of further clarifying the genetic relationship between two social forms of Solenopsis invicta. Such social forms are common in many groups of ants and may, in some cases, represent significant intermediate stages in the speciation process. The monogyne and polygyne forms of S. invicta, while differing in a number of important biological traits, are genetically indistinguishable, in contrast to the substantial genetic differentiation observed between S. invicta and a second, closely related, introduced species, S. richteri. The native fire ant, S. geminata, is genetically the most distinct of the three species studied, in accord with its taxonomic placement in a different species complex. Hypotheses concerning the derivation of the polygyne form of S. invicta from the monogyne form which invoke their long-term reproductive isolation in South America and separate introductions to North America appear unfounded. Although S. invicta and S. richteri are known to hybridize in North America, our study provided no evidence of gene introgression between S. invicta and the native species, S. geminata, in areas where our samples were collected. Analyses of population structure in S. invicta failed to reveal significant differentiation of populations or local inbreeding. Levels of genetic diversity in the three species studied, although not significantly different, were in the order predicted from knowledge of the population biology and recent history of the taxa, with S. richteri exhibiting the least diversity, S. geminata the greatest, and S. invicta having an intermediate level.

Developmental stability, heterozygosity, and fitness in two introduced fire ants (Solenopsis invicta and S. richteri) and their hybrid

“…As expected given that (1) the parental populations are fixed for alternate alleles at three loci, and (2) no evidence for large-scale departure from panmixis has been found (Ross et aL, 1987a,b; see also below), the hybrid popula- tions have a higher proportion of polymorphic loci than do the parental populations, as well as generally higher levels of heterozygosity (P = 0065 for the comparison between S. invicta and the MS hybrid population). Heterozygosity values for S. invicta and S. richteri are virtually identical to earlier estimates based on more complete samples (Ross et a!., 1987a).…”

“…Alternatively, these findings may represent a more general feature of natural populations of social Hymenoptera. A growing body of data indicates that these insects (including native Solenopsis) are relatively deficient in genetic variability (and thus heterozygosity) as determined electrophoretically (Graur, 1985;Sheppard and Heydon, 1986;Ross et a!., 1987a;K. Ross and J. Trager, unpublished), and a decreased capacity for genetic buffering of development may accompany this low heterozygosity if such buffering is achieved largely via overdominance.…”

A Reanalysis of Diploid Male Frequencies in Euglossine Bees (Hymenoptera: Apidae)

“…We therefore found no evidence that expected mean heterozygosity at allozyme loci in Brazilian euglossine bees (0.03 Ϯ 0.006 SE) differs significantly from that of other Aculeata Hymenoptera (0.05 Ϯ 0.009 SE, n ϭ 39; data from Graur 1985; Kukuk and May 1985;Ross et al 1987;Packer and Owen 1990;Shoemaker et al 1992;Kukuk and Sage 1994;Rosenmeier and Packer 1993) (twotailed Mann-Whitney test, Z ϭ 1.50; P Ͼ 0.10).…”

Relatedness and inbreeding in a French population of the unicolonial antIndomyrmex humilis (Mayr)

“…It is interesting to note that in the polygynous form of Solenopsis invicta, as in L hurnilis, sexual dimorphism (i.e. size differences between sexes) is low, and that, as in L humilis, the inbreeding estimate is close to zero (Ross et al, 1987).…”