SYMPATRIC SPECIATION IN SNAILS; A LARGELY NEGLECTED MODEL

摘要: Usually, shells of snails are clearly either dextral or sinistral. That means that, if one looks at the apex, whorls increase in width clockwise counterclockwise, respectively. In a shell, soft parts animal have proximal part genitalia situated asymmetrically right side head. Most species dextral, clear minority sinistral, and few polymorphic ifor direction coiling. many aberrant specimens opposite coil known (for additional information, see Johnson [1982] Gould et al. [1985]). Reproductive isolation can be consequence The various degrees cases studied until now depended upon differences interspecific behavior shell shapes. three which observations show that animals cannot copulate (see below), characterized by globular equals exceeds height. Partula sutoralis, has more slender, relatively higher shells, copulation is hindered but not prohibited (Lipton Murray, 1979; Johnson, 1982). For Laciniaria biplicata, with very slender we know mirror-image how readily they do so (Degner, 1952). A realistic model for sympatric speciation received much attention English literature, perhaps because some underlying notes been published Dutch, German, Russian. Meisenheimer (19 12 p. 131) stated sinistral specimen helicid gastropod Helix pomatia will try to vain: ". . days weeks fatigue each other courtship, without achieving final copulation." Hesse (1914) reported both aspersa, copulations between individuals proved impossible interfered. This author suggested might less dramatic consequences possessing them. Janssen (1966) detailed concerning Arianta arbustorum (which broad shell), kept months same species. Several times, he observed tried copulate, these attempts were always success, genital pores could never come into contact. Both produced unfertilized eggs. These facts brought Gittenberger (1973 1) state "the fact may underlie mechanism resulting speciation." Alexandrov Sergievsky (1979) dealt on basis chirality. They distinguished four stages process: mutant recessive genes only present heterozygotes manifest themselves; 2) phenotype appears; 3) stable population formed; 4) new enlarge its range. Stages require allopatric populations. main question whether develop within cruising range normal specimens. (1982) also described several possible components work Partula, including chirality clines assortative mating. move short distances after hatching, therefore, inbreeding common. increases likelihood stage 2 being reached. Because so-called maternal delayed inheritance, found genetically (all Pulmonata), up next generation, those from eggs homozygote (Boycott al., 1930; Degner, 1952; Murray Clarke, 1966). genotype parent decisive coiling young. As consequence, snail itself homozygous coiling, when heterozygous dominant. Its individuals, however. result this form gene flow still population, even different phenotypes copulate. stop as soon homozygotes occur. Selection favoring probable, offspring will, average, lower probability finding optimal sexual partners nearby. Pulmonate snails, hermaphrodites, capable self-fertilization, frequency nature largely unknown. fewer young than usual mixed pairs where such rare. He does mention allelic compositions involved. natural selection, it would interesting reduced fertility. ( 1982) argued there selection against rare coil, thus monomorphism. strongest mating impossible. Despite this, low dispersal, locally strong inbreeding, and/ genetic drift, morph occasionally