The Chromosomes of Neotropical Butterflies from Trinidad and Tobago

Abstract

Chromosome numbers and karyotypic observations are reported for 27 species of neotropical Lepidoptera in 8 families (Satyridae, Ithomiidae, Nymphalidae, Papilionidae, Pieridae, Lycaenidae, Riodinidae, and Hesperiidae). Characteristic haploid numbers for certain genera are found: Parides (N=30 or 31), Phoebis (N=31), Eurema (N=28, 29, 30, or 31), Dynamine (N=29 or 30), Mestra (N=31 or 33), Anartia (N=31) and Agraulis (N=31). Two genera showing widely varying chromosome numbers are Heliconius (N=19, 20, 21, 22, 24, 25, 26, 27, 28, 29, 30, 33, 38, and 56) and Mechanitis with (N=16, 17, 18, 19, 21, 24). The butterflies in these genera are involved in extensive mimicry complexes. The occurrence of fragmentation in Heliconius and AMechanitis may play a role in promoting ease of genetic recombination, which in turn could increase the diversity of phenotypes in the population and influence effects of natural selection. THE ISLANDS OF TRINIDAD AND TOBAGO, 10 miles off the east coast of Venezuela, provide a varied series of tropical lowland and montane habitats for some 617 species of butterflies (Barcant 1970). Numerous studies on the behavior and genetics of several lepidopteran groups have been carried out at the Arima Station of New York Zoological Society (e.g., Crane 1955). However, little information is available on the karyotypes of these species. De Lesse (1967, 1970) has published chromosome counts on species from Central America and northern South America, which include a few subspecies of species also found on the islands of Trinidad and Tobago. Suomalainen et al. (1972) give haploid numbers for 14 heliconiine butterflies found in Trinidad. The purpose of this paper is to report chromosome numbers and karyotypic observations for 27 species of eight butterfly families (Satyridae, Ithomiidae, Nymphalidae, Papilionidae, Pieridae, Lycaenidae, Riodinidae, and Hesperiidae) from Trinidad and Tobago. MATERIALS AND METHODS All material studied in this report was collected by the authors on the islands of Trinidad and Tobago during the month of September 1970. Testes of live, wild-caught males were removed with fine dissecting forceps and fixed in vials containing 3:1 alcohol:acetic acid (Emmel 1969). Upon returning from the field the vials containing the testes were stored at -20?F until processing in the Gainesville laboratory. For microscopic observation, testes were stained with lacto-aceto-orcein, and squashed under a press until the testicular material was approximately one cell layer thick. Preparations were examined with a Carl Zeiss Research Microscope Standard WL fitted with 25x, 40x, and 1OOx planapochromatic flatfield objectives and automatic camera (refer to Emmel 1969 for further details). All uniformly spread metaphase plates of each individual were counted in order to verify the count and determine any variance within a particular specimen. Additional observations were made under phase contrast using a Watson Photoautomatic Phase Contrast Microscope Hilux 70 pH fitted with 40x Planpara and 90x Fluorite phase contrast objectives and automatic camera. It may be noted that many examined specimens lacked dividing cells. In some species, spermatogenesis may be largely completed in most of the individuals at the time of eclosion, therefore making it difficult to observe divisions in a wild-caught adult unless caught and preserved immediately upon emergence. Alternately, some of the butterflies of these islands may be seasonal in gamete production. Heliconius, for instance, are known to have a life span of up to six months (Benson 1972; Benson and Emmel 1973; Ehrlich and Gilbert 1973). It would be possible, therefore, that certain species were not undergoing meiotic divisions at the time of capture since collections were made only in the middle of the wet season.