Reproductive isolation

Lepidoptera is the second largest insect group and includes nearly 150,000 described species, which have evolved over 100 million years since the Mesozoic era. For the birth of a new species, it must be isolated from other species by some factor to prevent inter-species crossing. The sex pheromone, which is secreted by the adult (usually by a female moth and sometimes by a male moth or butterfly) for the benefit of a specific partner, plays an important role in reproductive isolation. Therefore, it is no wonder that the chemical structures of the species-specific pheromones exhibit considerable differences. 

Contrary to the structure similarity of the pheromones secreted by taxonomical related moths, some differences are necessary for their sexual communication systems to play an important role in their reproductive isolation. In addition to further modifications of the various structures, diversity of the lepidopteran sex pheromones is generated by blending multiple components. Innumerable pheromone blends are based not only on combinations of different components but also on variations in the mixing ratio. A pioneer study with Adoxophyes spp. (Tortricidae Tortricinae) had already proposed this concept in the early 1970s. While the smaller tea tortrix (A. honmai) and the Japanese summerfruit tortrix (A. oranafasciata) had been considered to be variant strains with different host preferences in the same species, Tamaki et al. found that females of the former pest insect in the tea garden secreted Z9-14 OAc and Zll-14 OAc in a ratio of 7 4 but females of the latter defoliator of apple trees secreted them in a ratio of 13 4 [127,128]. Furthermore, two other components (Ell-14 OAc and MelO-12 OAc) were subsequently identified from the former species [129]. 

It is also important to understand the source and significance of genetic variations. The Pima Indians have the highest rates of diabetes in the world Tay-Sachs disease is primarily found in Ashkenazi Jews. Contemporary literature indicates that these differences stem from reproductive isolation, not race. Genetic traits common to persons with sickle-cell disease are related to malaria frequency and not our social view of race. This is why the disease can be found in high frequency in Yemen, West Africa, Greece, and Saudi Arabia. 

Discrimination of species odors, and hy inference, reproductive isolation between species by means of odors, has been demonstrated for many species. Early examples are bank voles, Ckthrionomysglareolus (Godfrey, 1958), Peromyscus spp. (Moore, 1965 Doty, 1972),M sspp. (Bowers and Alexander, 1967), andger-bils (Dagg and Windsor, 1971). Male naked mole rats (superspecies Spalax ehren-hergi, Spalacidae) preferred odors from estrous females of their own to a different karyotype in a two-choice apparatus. The odors used were those of soiled bedding and urine from females (Nevo etah, 1976). 

In addition to their role in orientation behavior, the periplanones may participate in reproductive isolation among sympatric Periplaneta species. Periplanone-A from P. americana attracts Periplaneta australasiae. Periplanone-B, and possibly some other components, inhibits attraction of male P australasiae (Seelinger, 1985b). Two other periplanones, periplanone-C (3 Table 6.2) and periplanone-D (4 Table 6.2), have been isolated from P. americana (Biendl et al, 1989 Takahashi et al,... 

Phelan, P. L. and Baker T. C. (1987). Evolution of male pheromones in moths reproductive isolation through sexual selection Science 235 205-207. 

Carde, R. T. (1987). The role of pheromones in reproductive isolation and speciation of insects. In Evolutionary Genetics of Invertebrate Behavior, ed. M. D. Huettel. pp. 303-317. New York Plenum. 

Collins, M. M. and Tuskes, P. M. (1979). Reproductive isolation in sympatric species of dayflying moths (Hemileuca Saturniidae). Evolution 33 728-733. 

Lofstedt, C., Herrebout, W.M. and Menken, S.B.J. (1991). Sex pheromones and their potential role in the evolution of reproductive isolation in small ermine moths (Yponomeutidae). Chemoecology 2 20-28. 

Monti, L., Gdnermont, J., Malosse, C. and Falanne-Cassou, B. (1997). A genetic analysis of some components of reproductive isolation between two closely related species, Spodoptera latifascia (Walker) and S. descoinsi (Lalanne-Cassou and Silvain) (Lepidoptera Noctuidae). Journal of Evolutionary Biology 10 121-134. 

Evolution of male pheromones in moths reproductive isolation through sexual selection. Science 235 205-207. 

Hybridization has retained oaks a model taxon for species concepts that rely on ecological criteria rather than on reproductive isolation [65]. The high similarity in chemical constitution of different oak pollens, which is verified by a very similar biochemical fingerprint in our Raman experiments, can be interpreted as part of the very weak barriers to being pollinated by another (oak) species. 

Peripheral variety is the product of primordial repetitive and reiterative polymerization of nucleic acids, i.e., a contiguous process Variety is the product of biological phenomena, i.e., gene duplication, mutation and selection, and reproductive isolation, i.e. a non-contieuous process. 

In all the chemolocation assays with pea crabs, the attraction of crabs from each host race to their respective host was substantially less than 100%, and some crabs chose incorrect hosts, suggesting that there may still be at least the potential for gene flow among populations. These experiments were conducted with adult crabs, and host location experiments with larval or post-larval forms that are normally responsible for initial host selection might be particularly informative. Nevertheless, this series of studies suggests that within-species differences in chemically mediated host location may lead to population subdivision and reproductive isolation among marine species. 

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