The Value of Cytogenetics for the Taxonomy and Evolution of Leaf Beetles (Coleoptera, Chrysornel Idae)
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Miscel.lania Zoologica 20.1 (1997) 9 The value of cytogenetics for the taxonomy and evolution of Leaf Beetles (Coleoptera, Chrysornel idae) E. Petitpierre Petitpierre, E., 1997. The value of cytogenetics for the taxonomy and evolution of Leaf Beetles (Coleoptera, Chrysomelidae). Misc. Zool., 20.1: 9-18. The value of cytogenet~csfor the taxonomy and evolut~on of Leaf Beetles (Coleoptera, Chrysomebdae) - The advantages and pitfalls of cytogenetics for the taxonomy and evolution of Leaf Beetles are discussed Karyology may provide clues for distinguishing cryptic sibling species as demonstrated in Chrysol~naaur~chalcea and Casslda v~r~d~sThe phylogenetic value of karyotypes can only be substantiated on the grounds of three general rules extensive sampling to determine the most widespread karyotype or meioformula, the criterion of parsimony, and parallel evolution of other characters A modal karyotype cannot be equalized a prior1 to the most primitive karyotype Hence, for simple effects of sampling, in a few Leaf Beetle subfamilies only the ancestral karyotype can be reasonably assessed The Chrysomelinae subfamily is studied in significantly greater detall, and the probable interrelationships of their higher taxa based on the chromosomal findings and their correlation with other characters of phylogenetic interest is discussed The presumed effects of deme size and specialized phytophagy on the karyological evolution of Chrysomelinae genera are also dealt with Key words: Cytogenetics, Leaf Beetles, Chrysomelinae, Taxonomy, Evolution. (Rebut: 10 1 97; Acceptació definitiva: 11 111 97) Eduard Petltplerre, Lab de Genetlca, Dept de Blolog~aAmb~ental, Unlv de les llles Balears- UIB, 07071 Palma de Mallorca, Espanya (Spa~n) This work was supported by project DGICYT PB93-0419, Ministry of Education and Culture, Spain. O 1997 Museu de Zoologia Petitpierre lntroduction species is its karyotype, defined by chromo- some number, size and morphology of each The Chrysomelidae or Leaf Beetles are one of individual chromosorne, and when pre- the largest farnilies of Coleoptera with some sent, such as in most animals, the type of 35,000 described species, and probably a sex-chromosome system. The karyotype of great number as yet undescribed (LAWRENCE,a species is usually constant and can there- 1982; JOLIVET & COX, 1996). This is the most fore be considered as a definite element, irnportant taxon of the superfarnily Chryso- like any morphological character, for taxo- meloidea, where Cerambycidae and Bruchi- nomic purposes. dae are also included among a total of five A simple manner to determine the rough families (CROWSON,1981). karyotype of a beetle species is by the The recent publication of three books rneioformula or karyotypic formula, the dealing with the biology of Chryso- number of autosomal bivalent plus the type melidae, in the broadest sense (JOLIVET of sex-chromosome system, usually obtained et al., 1988, 1994; JOLIVET & COX, 1996), from males, at rneiotic metaphase I (SMITH& and specially several of its chapters dedi- VIRKKI,1978). Thus, a rneioformula of 9+Xyp, cated to the phylogeny and evolution of means nine autosomal bivalent and a sex- the group, has given rise to considerable chromosome bivalent made up of a large X interest in these subjects from a multidis- and a small y, noted by a capital letter and ciplinary view. Two authors specialized in a srnall letter respectively, held together by Leaf Beetles recently questioned the use- a 'parachute' (p) type of association, be- fulness of cytogenetics as a suitable tool cause it resernbles this configuration. Equal- for phylogenetic and evolutionary studies. ity of meioformulas between two species CROWSON(1994) stated that 'chromo- does not mean they have identical karyo- somal patterns do not usually provide reli- types. If this were true the huge nurnber able markers for higher taxa ,... marked of beetles with the modal 9+Xyn rneioformula karyotypic differences may be found be- would be indistinct in theii karyotypes, tween species which in other respects seem which is clearly nonsense. In fact, alrnost al1 closely allied, and very similar karyotypes sisecies can be differentiated in their can persist in extensively varied groups', to karyotypes provided they are surveyed conclude 'the main systematic (and biologi- through a high resolution analysis, narnely cal value) of karyotypic studies is likely to by chromosome banding, in situ hybridiza- be around the level of species, as demon- tion, and a deep study of meiosis. The only strated e.g. by Virkki's studies in Alticinae'. known exceptions to this rule in animals In addition, REID (1995) did not use (just over 1%), are the homosequential spe- karyology among the 71 characters used in cies of Drosophila, whose polytenic chro- his long and detailed cladistic analysis of rnosomes enabled a high resolution analy- Leaf Beetles, because 'karyology tends to sis. They have identical patterns of bands consider common to primitive, but this is and are therefore impossible to distinguish unacceptable for several reasons, including (WHITE,1978). sample bias and failure to distinguish be- Specifically regarding Leaf Beetles, tween an ancestral state frorn one shared by closely related species can differ or not in a recent radiation of species', adding finally their meioformulas, but when they are co- that 'at present levels of study, kariology is incident even a conventional morphometric useless for chrysomelid phylogeny except at analysis of mitotic metaphase chromoso- trivial levels, as already noted by CROWSON mes, which is not an extremely power- (1981)'. Nevertheless the topic is worthy of ful technique, can demonstrate differences, more detailed study and discussion. as shown in two lndian species of Cassida (YADAV& PILLAI, 1975), the allied species of Chrysolina feeding on Labiatae plants The value of karyotype for the taxonomy (PETITPIERRE,1983), and 13 North American of Leaf Beetles Leptinotarsa (HSIAO& HSIAO,1983). Both CROWSON(1994) and REID (1995) One characteristic of the phenotype of a agree in the acceptance of the karyotype Miscel.lania Zoologica 20.1 (1997) as a valuable character to species tax- The karyotype as a phylogenetic character onomy. Nevertheless, and contrary to the latter author, the species level is not at al1 Phylogeny implies recognition of polarity trivial for taxonomy and phylogeny, ei- and the modern and extensive cladistic ther in basic or in applied research, and analyses in Leaf Beetles assume ances- several examples could be quoted to sup- tral (plesiomorphous) and derived (apo- port this view. morphous) states in many characters to Two recent findings illustrate the value build up the most parsimonious trees, of karyotype for taxonomy and phylo- phenograms or cladograms (LEE,1993; REID, genetic interrelationships. The first is rep- 1995). Likewise, cytogenetic data may be resented by the complex of taxa known as used in phylogenetic studies if polarity of Chrysolina aurichalcea from Japan and Korea, change is reasonably inferred. Before dis- whose existence was proved by karyotypic cussing how to answer the question of analysis showing distinct chromosomal races, polarity in evolutionary cytogenetics, sev- with n=32, 2n=42 and 2n=46 diploid num- eral important premises should be clearly bers, that should be rightly consider- settled. First of all, there is not a prior; ed as sibling species (PETITPIERRE,1981; FUJI- reason for assuming that extant species YAMA, 1989). The spermatids of siblings with with primitive morphology, behaviour and n=16 and n=23 chromosomes had no sig- life history should also have the most primi- nificant differences in their DNA content, tive karyotypes. This may occur or not, be- so, the chromosomal shifts involved in cause evolution proceeds in a mosaic way the origin of the latter from the former, with some characters being derived and 0th- according to the common trend found for ers conserved with respect to the ancestral the genus, have not changed this param- state. A correspondence between karyotype eter (PETITPIERREet al., 1991). A second and evolutionary ancestry could be true if example of siblings was found in the tor- the cytogenetic characters determine, at toise beetle Cassida viridis, the spe- least to some degree, the states of the cimens from Switzerland and from Catalo- non-cytogenetic characters, andlor if the nia (NE Spain), dsiplayed 2n=24, while those rates of karyotypic change and those of from two geographical sources in Andalucia other characters are correlated across (S Spain) had 2n=30 chromosomes (PETITPIERREevolving lineages. Consequently, the et al., 1988, in prep.). Whereas the adults cytogenetic characters cannot be taken of Chrysolina aurichalcea siblings show alone in phylogenetic analyses, especially slight differences in male genitalia and eco- in taxonomic categories higher than ge- logical niches (FUJIYAMA,1989; FUJIYAMAet al., nus. They can serve to test phylogenetic 1991; FUJIYAMA & TAKANASHI,1994), those of hypotheses principally based on exo- Cassida viridis siblings are identical but phenotypic characters, that is morphologic their larvae have not as yet been' studied and behavioural traits, and this is their and might provide some clues for distinc- main evolutionary usefulness. tion. But how can we determine the direc- Greater efforts should be directed to tion of karyotypic change between two the karyological characterization of Leaf states A and B: A -> B or B -> A? A Beetle species by using conventional common practice,