Sex-Linked Genes and Species Differences in Lepidoptera

Abstract

The Canadian Entomologist 126: 807-818 (1994) I review reports on the genetic basis for species differences in the Lepidoptera. In the six best-studied species complexes, more than half of all ecological, behavioral, or physiological differences among species are controlled by X-linked genes. Because Lepidoptera have about 30 pairs of chromosomes, this finding clearly indicates strong bias toward X-linkage of genes for species differences. The proportion of X-linked species differences ranges from complete X-linkage in Colias butterflies, to almost none in Yponomeuta moths. Four other complexes all have at least one X-linked gene that is crucial to species differences, including the Choristoneurafumiferana Clemens, Papilio glaucus L., and Papilio machaon L. species groups, and Ostrinia nubilalis Hiibner pheromone strains. The mechanisms that account for this phenomenon are open to speculation. Nonetheless, an interesting implication of disproportionate X-linkage is that reproductive isolation may frequently arise by selection on linkage complexes, rather than as a random byproduct of evolution in geographically isolated populations. If confirmed, the bias toward X-linked species differences may also help efforts to find characters that distinguish host races and sibling species, as well as provide an avenue by which genes crucial to speciation can be more easily mapped and characterized at the molecular level. Sperling, F.A.H. 1994. Genes reliks aux chromosomes sexuels et diffkrences spkcifiques chez les Upidopthes. The Canadian Entomologist 126: 807-818. Resume J'ai fait la synthbse des donnks sur l'origine gCnCtique des diffkrences spCcifiques chez les Upidoptbres. Chez les six complexes d'espbces les plus CtudiCs, plus de la moitiC de toutes les differences Ccologiques, comportementales et physiologiques entre les espbces sont attribuables B des gbnes liCs au chromosome X. Comme les LCpidopthres ont environ 30 paires de chromosomes, cette constatation indique clairement que les differences spkcifiques sont fortement reliCes au linkage B 1'X des diffkrents gbnes. La proportion des diffkrences spCcifiques likes h 1'X va de 100% chez les espbces de Colias, B prbs de 0% chez les papillons nocturnes du genre Yponomeuta. Quatre autres complexes ont tous au moins un gbne liC B 1'X qui est essentiel aux diffkrences spCcifiques, notamrnent les groupes d'espkes de Choristoneura furniferana Clemens, de Papilio glaucus L. et de Papilio machaon L., et les lignks d'ostrinia nubilalis Hiibner diffCrenciCes par leurs phCromones. Les mCcanismes responsables de ce phCnombne sont mal connus. Cependant, l'un des corollaires intCressants de l'hypothbse d'un linkage B l'X disproportionnC suppose que l'isolement gCnCtique est souvent le rCsultat de la sClection de complexes de linkage plut6t que le produit alCatoire de l'kolution chez des populations isolCes gkographiquement. Si cette hypothbse est confirmCe, l'attribution des diffkrences spCcifiques aux gbnes liCs B 1'X peut Cgalement rendre plus facile la dktermination de carac...

Genetic mapping of Z chromosome and identification of W chromosome-specific markers in the silkworm, Bombyx mori

“…Interspecific hybridization of many species of wild silk moths has revealed that many reciprocal crosses result in sterile F 1 offspring (Jolly et al, 1969;Nagaraju and Jolly, 1985;Shimada and Kobayashi, 1992). Recent studies in other Lepidoptera have shown that the Z-linked genes associated with mating preferences may play a role in host race formation (Sperling, 1994) and speciation (Iyengar et al, 2002). Female F 1 offspring produced in interspecific crosses between two species of sexually dimorphic Colias butterflies prefer to mate with males of the paternal species, indicating that Z-linked genes played a role in their speciation (Grula and Taylor, 1980).…”

“…Characteristics affecting reproductive isolation and host race formation appear to be predominantly sex linked in many groups of lepidoptera (Sperling, 1994). Thus, analysis of Z-linked genes especially those controlling maturity, diapause, body size, etc.…”

Inheritance and linkage of isozymes in Yponomeuta padellus (Lepidoptera, Yponomeutidae)

“…The highly polymorphic 6pgdh, however, had been explicitly rejected as a sex-linked locus in crosses of Y cagnagellus (Menken, 1980b). This shows that sex-linkage groups in the two closely related species are not completely conserved, and adds another level of complexity in assessing the role of sex-linked loci in reproductive isolation and host-race formation as suggested by Sperling (1994).…”

“…The first is to establish which allozymes are sex-linked in Y padellus. In a recent review, Sperling (1994) pointed out that in many groups of Lepidoptera, characteristics affecting reproductive isolation and host race formation appear to be predominantly sex-linked. However, he identified Yponomeuta as a group to which this generalization did not apply (see Van Drongelen & Van Loon, 1980;Hendrikse, 1988).…”

Host Plant Specialization Driven by Sexual Selection

“…We consider the case of Z linkage for oviposition preference genes because all studies of such genes in butterflies show sex linkage (Sperling 1994;Janz 1998;Prowell 1998 Host plants a and b can differ in one of two ways, either by the presence in a of a unique chemical that can be later modified into a mating pheromone or in the relative ratios of the same host plant chemicals that go into making the pheromonal suite of the adult male. Males developing on a host plants experience increased fitness relative to males developing on host plant b, reflecting the attractiveness of the pheromone in the adult stage and a preexisting preference in females for this pheromone.…”