EVOLUTIONARY IMPLICATIONS OF CHROMOSOMAL HOMOLOGY IN FOUR GENERA OF STENODERMINE BATS (PHYLLOSTOMATIDAE: CHIROPTERA)

Transcription

1 Evolution, 33(1), 1979, pp EVOLUTIONARY IMPLICATIONS OF CHROMOSOMAL HOMOLOGY IN FOUR GENERA OF STENODERMINE BATS (PHYLLOSTOMATIDAE: CHIROPTERA) ROBERTJ. BAKER, REBECC A. BASS AND M. ANETTE JOHNSON The Museum and Department of Biological Sciences, Texas Tech University, Lubbock. Texas Received January 16, Revised May 26, 1978 Phylogenies based on similarity of standard karyotypes of representatives of 17 of the 18 stenodermine (Stenoderminae: Phyllostomatidae) genera have been published (Baker, 1973; Greenbaum et al., 1975; Gardner, 1977). The phylogenies of Baker (1973) and Greenbaum et al. (1975) are based on the supposition that the primitive karyotype for the subfamily had a 2n = 30 or 32 and a fundamental number of The phylogeny of Gardner (1977:313) is based on the assumption that the primitive karyotype for the subfamily had a "diploid number near or above 40 and a low fundamental number." A G-banding study (Patton, 1976) of 10 genera in the subfamily Phyllostomatinae (and representatives of the Noctilionidae and Mormoopidae as well) revealed that the karyotype which requires the least number of convergent events to derive karyotypes of living forms consisted of a 2n = 46; FN = 60. Although Gardner's proposed phylogenies and the study by Patton do not prove that the primitive karyotype for the common ancestor of living stenodermine genera is higher than 30, they do raise a valid question as to the degree of homology of the biarmed chromosomes of the respective karyotypes of those forms with 28 autosomes. Also see the discussion by Hecht and Edwards (1976) on the problem of convergence and systematics. To obtain an assessment of the degree of homology among stenodermine bats, we have examined the G-banding pattern of the chromosomes of representatives of the genera Sturnira, Artibeus, Enchisthenes and Uroderma. We chose Sturnira and Artibeus because these two genera represent living species of two lineages that are presumed by Smith (1976) (based on dental and osteological characters) to share a common ancestor that could have given rise to all stenodermine genera. Additionally, Artibeus and Sturnira have autosomal complements that are similar in shape and number (28). If for each Artibeus autosome there is an identically banded autosome in the karyotype of Sturnira. then the autosomes are almost certainly the same as those possessed by the last common ancestor of these genera. However, if the karyotypes of these genera were independently derived from a karyotype like that proposed as primitive for the family Phyllostomatidae (with a 2n = 46, Patton, 1976 and 2n = 40, Gardner, 1977) then the similarity in number and morphology of the autosomes would be the result of convergence and the degree of banding homologyushould be low. Specimens of the 2n = 44 cytotype of Uroderma bilobatum were examined because this is the karyotype most like that proposed by Gardner (1977) as primitive for the subfamily. Gardner proposes that such a karyotype underwent pericentric inversions (and possibly additions of heterochromatin) to produce a 2n = 30; FN = 56 karyotype. We examined Enchisthenes to determine how it differed from Artibeus, the genus to which it is most closely related. C-banded karyotypes from these species were studied to determine whether addition of heterochromatic arms was responsible for any of the au-

2 CHROMOSOMAL HOMOLOGY IN BATS 221 A S E I xx xyxx FIG.1. G-banded karyotypes of Artibeus jamaicensis (column A), Sturnira lilium (column S) and Enchisthenes harti (column E). Autosomal pairs are labeled 1-14 for identification in text.

3 222 R. J. BAKER ET AL. tosomal arms found in species with higher fundamental numbers. METHODSAND ATERI RIALS G- and C-band preparations were made from tissue-cultured fibroblasts grown from ear and lung in Ham's F-10 media, supplemented with percent fetal calf serum. G- and C-band techniques are described by Patton (1976). Several G- and C-banded spreads were examined and compared for each specimen examined. Chromosome pair 9 (Fig. 1) is easily identified and occurs in the karyotypes of all four genera. Variations in the stage of contraction of homologous elements were standardized by enlarging each karyotype printed to a standard size for chromosome pair 9. Homologous pairs of autosomes in the 2n = 30 forms are numbered 1-14 for the convenience of discussion; however, these numbers do not cross-reference to the numbering system of arms in Macrotus as described by Patton (1976) and Baker (1979). Specimens examined.sturnira lilium (1 male), Trinidad, St. George, Blanchisseuse; Artibeus jamaicensis (3 females), Tamaulipas, 2 km N Tampico, and Venezuela, Guarico, 55 km S Calabozo; Enchisthenes harti (2 females), Venezuela, Miranda, 24 km N Altagracia; and Costa Rica, Alajuela, 2.5 mi SSE Cariblanco; Uroderma bilobatum (1 male and 1 female), El Salvador, Usulatan, 3 mi E Usulatan. Voucher specimens are deposited in The Museum, Texas Tech University. G-banded karyotypes of Artibeus jamaicensis (columns labeled A), Sturnira lilium (columns labeled S) and Enchisthenes harti (columns labeled E) are shown in Figure 1. The G-banding patterns of Artibeus chromosomes are sufficiently unique that in good preparations pairs 1, 2, 3, 4, 5, 9, 10, 12 and 13 can be unequivocally identified. Pair 6 is difficult to distinguish from pair 7; however, elements are easily identified as either pair 6 or 7. The same is true for pairs 8 and 14. Pair 14 is the smallest pair but even this distinction is sometimes difficult to determine. Pair 11 is difficult to distinguish from the X chromosomes, but these elements are easily distinguished from all others. Comparison of A. jamaicensis and S. lilium reveals that elements 1, 2, 3, 4, 5, 9, 10, 12 and 13 have identical G-banding patterns. In all Artibeus and Sturnira examined, there are four chromosomes referable to the 6 and 7 elements. After identification of the X and Y in the Sturnira karyotype, there remain elements that appear homologous to chromosome 11 of Artibeus. The major difference between the two karyotypes is in the 8 and 14 complex. In Artibeus, both 8 and 14 have a medially placed centromere, whereas in Sturnira one has a medially placed centromere (pair 14 in Fig. 1) and one is subtelocentric (number 8). This difference is best explained by a pericentric inversion. Because the two smallest chromosomes in some species of Sturnira and all Artibeus examined are metacentric, the subtelocentric number 8 of Sturnira is probably the derived condition. The standard karyotype of Enchisthenes harti differs from that of Artibeus (Baker, 1967) by having only 8 pairs of metacentric or submetacentric autosomes (as opposed to 10 in Artibeus) and 6 pairs of subtelocentric elements (4 in Artibeus). The G-banded karyotype of Enchisthenes (Column E, Fig. 1) reveals that this difference is best explained by a single reciprocal translocation. There are no detectable differences between the G-banding patterns of the Artibeus and Enchisthenes chromosomes However, the karyotype of Enchisthenes can be derived from that of Artibeus by a reciprocal translocation involving pairs 13 and 14 (or perhaps 8 instead of 14), changing a medium (pair 13) and a small sized metacentric (pair 14) to two medium sized subtelocentrics (shown beside pair 13 in Fig. 1). There is considerable difficulty in relating much of the Artibeus karyotype to that of the 2n = 44 cytotype of Uroderma bilobatum (Fig. 2). Only two elements (num-

4 CHROMOSOMAL HOMO1,OGY IN RATS 223 FIG. 2. G-banded karyotypes of Artibeus jamaicensis compared to the 272 = 44 cytotype of Croderma bilobatum. Artibeus chromosomes are labeled according to their number in Fig. 1. All chromosome not labeled with an A are from Uroderma. bers 9 and 12) appear to have been unal- the variation between chromosomes 2, 3, tered since the two genera last shared a 4, 6 and 13 and their acrocentric countercommon ancestor. Each of the biarmed parts in Uroderma. In pair 1 there seems chromosomes 1, 2, 3, 4, 6 and 13 of Ar- to be more material near the centromeres tibeus (Figs. 1 and 2) match two acrocen- in the acrocentrics from liraderma than trics from Uroderma. A simple Robert- is present in the biarmed element of Arsonian fusion-fission is adequate to explain tibeus. Consequently, some additional

5 224 R. J. BAKER ET AL. FIG.3. C-banded karyotype of Enchisthenes ha? *ti. Dark centromeric regions are C-band material. event other than the Robertsonian one is needed to explain the differences. The long arms of chromosomes 5, 7 and 10 of Artibeus appear to be homologous to three acrocentrics from the Uroderma karyotype. In pair 10 (Fig. 2) the terminal portion of the Uroderma acrocentric contains much more material than is found in the long arm of 10. Pairs 8, 11 and 14 of Artibeus are not easily related to the remaining Uroderma chromosomes. Pairs 8 and 14 of Artibeus are small biarmed elements. The 2n = 44 cytotype of Uroderma has a similar pair. In Figure 2, this Uroderma pair is unlabeled and to the right of Artibeus 14. If the Uroderma biarmed pair is homologous to either the 8 or 14 of Artibeus, G-banding does not fully suggest it. Neither 8 nor 14 have the double dark bands characteristic of the Uroderma pair. The acrocentric Uroderma chromosomes to the right of pair 11 may be related to the biarmed elements of Artibeus by a pericentric inversion. However, there are not enough distinct bands on these chromosomes to convincingly demonstrate such a change. Two Uroderma pairs (bottom row, Fig. 2) have no obvious relationship to any of the Artibeus chromosomes. C-banding revealed no heterochromatic arms in the karyotype of A. jamaicensis, S. lilium, E. harti or U. bilobatum. A C-banded karyotype of Enchisthenes is shown in Figure 3. A. jamaicensis, S. lilium and U. bilobatum have similar distributions of heterochromatin. Very little heterochromatin was detected in C-banded chromosomes from -Sturnira. Chromosomal similarities between the standard karyotypes of Artibeus and Sturnira are not the result of convergence. If these two genera represent an old divergence in phyllostomatid evolution (as suggested by their placement in separate subfamilies, Miller, 1907), then the 2n = 30; FN = 56 karyotype was probably primitive for the line that gave rise to all stenodermines. If, on the other hand, these two genera shared a common ancestor after the ancestors of other genera (such as Uroderma, Centurio, and Phyllops) had diverged from the Artibeus- Sturnira line, then the possibility of a 2 n = 40; FN = near 40 ancestral karyotype remains a possibility (Gardner, 1977). That Uroderma has the derived condition is also supported by data discussed below. There are more biarmed chromosomes shared between the karyotypes of Mac-

6 CHROMOSOMAL HOMOLOGY IN BATS 225 rotus (Patton, 1976) and Artibeus than are shared between Uroderma and Artibeus. Pairs 2, 4 and 5 of Artibeus are homologous to pairs 112, 415 and 617, respectively, of Macrotus (Baker, 1979). Further, it appears that pairs and of Macrotus (Baker, 1979) are homologous to pairs 6 and 7 of Artibeus. No biarmed pairs are shared between the karyotypes of Uroderma and Macrotus. About 10 pairs of acrocentrics do appear to be shared, but positive identification of some of these acrocentric elements is difficult. Only two complete chromosomes are shared between Artibeus and Uroderma, which means that 85 percent of the autosomes of Artibeus would have to be rearranged to derive the Uroderma karyotype. So many rearrangements do not distinguish the autosomes of Macrotus (Family, Phyllostomatidae), Pteronotus (Family, Mormoopidae) and Noctilio (Family, Noctilionidae) from each other (Patton, 1976). Five of the eight biarmed autosomes believed to be primitive for the family Phyllostomatidae (Patton, 1976) appear to be preserved in the karyotype of Artibeus and Sturnira but not in Uroderma. Therefore, it seems more parsimonious to hypothesize that these elements reflect the primitive condition in Artibeus and Sturnira and represent a derived condition in Uroderma. It is possible that some of the acrocentrics shared by Macrotus and Uroderma are primitive for the Stenoderminae. We see no aspect of our G- and C- banding data that refutes the FN = 60 primitive phyllostomatid condition for the family as suggested by Patton (1976). Our C-banding data clearly demonstrate that if a low FN was characteristic of the primitive karyotype for the subfamily, the fundamental number was not increased by the addition of heterochromatic arms as has been suggested as an alternative to pericentric inversions (Gardner, 1977:313). Our data from these four genera suggest that chromosomal data may be valuable in determining the evolutionary relationships of species that have questionable af- finities to the Stenoderminae, such as Brachyphylla. Subtelocentric chromosome pairs 9 and 12 (Figs. 1 and 2) are easily recognized and found in the four genera of stenodermines examined and are not found in the phyllostomatines (Patton, 1976), carolliines or glossophagines (Stock, 1975) studied. We believe that these two biarmed elements are derived, and their presence in the karyotype indicates a common ancestry with other stenodermine genera. Their presence in the karyotype of Sturnira further supports the conclusion (Baker, 1967) that Sturnira is a member of the Stenoderminae and does not deserve subfamilial distinctness. The fact that Enchisthenes varies chromosomally from all species of Artibeus (12 of 13 species in the genus have been studied for standard karyotypes, Baker, 1979) thus far studied sets it apart from the genus. We feel, however, that caution should be taken in order not to give these data too much weight in determining the validity of the genus Enchisthenes (see Baker, 1979, for a discussion on the use of chromosomal data in systematics). A single event, a reciprocal translocation, is adequate to explain the uniqueness of the Enchisthenes karyotype from that of Artibeus. It is obvious that chromosomal events do not occur at a constant rate in the evolution of phyllostomatid bats (Baker, 1979). It is possible that such an event could have occurred in the recent ancestor of a single species of Artibeus, Vampyrops, Sturnira, etc., without being adequate basis for giving that species generic status from other species in that genus. On the other hand, chromosomal distinctness must be added to the list of characters which make E. harti unique from species of Artibeus and in combination with other characters, may help justify generic distinctness. G-banding and C-banding analyses were performed on the chromosomes of Sturnira lilium, Artibeus jamaicensis, Enchisthenes harti and Uroderma bilobatum (2n = 44; FN = 48 cytotype) to

7 226 R. J. BAKER ET AL determine the degree of homology between these taxa. The karyotypes of A. jamaicensis and S. lilium differ only by a pericentric inversion in one pair of small autosomes. The karyotype of E. harti differs from that of A. jamaicensis by a reciprocal translocation involving two autosomes. The karyotype of Uroderma is different from Artibeus with only two pairs of autosomes and the X chromosomes in common. Two pairs of subtelocentric chromosomes are shared by all four genera but were not found in any of the other subfamilies of phyllostomatids previously studied. These two chromosomes may be valuable indicators of common ancestry for these and other stenodermine genera. These data are interpreted as further documentation that the genus Sturnira has a common ancestry with the Stenoderminae. ACKNOWLEDGMENTS We thank John Bickham, Laurie Erickson, Alfred L. Gardner, Ira Greenbaum, Rodney Honeycutt, and John Patton for critically reviewing this manuscript. We thank our colleagues for assistance in collecting specimens. T. C. Hsu and A. D. Stock provided technical assistance. We thank Sr. Tomas Blohm for field facilities and access to his ranch. Laboratory and some field research was supported by National Science Foundation Grant number DEB The specimens from Ven- ezuela were obtained through support provided by The International Environmental Sciences Program awarded to John Eisenberg. BAKER, R. J Karyotypes of bats of the family Phyllostomatidae and their taxonomic implications. Southwest. Natur. 12: Comparative cytogenetics of the New World leaf-nosed bats (Phyllostomatidae). Periodicum Biologorum 75: Karyology, p In R. J. Baker, J. K. Jones, Jr., and D. C. Carter (eds.), Biology of Bats of the New World Family Phyllostomatidae. Part 111. Spec. Publ. Mus., Texas Tech Univ., 16:l-144. GARDNER,A. L Chromosomal variation in Vampyressa and a review of chromosomal evolution in the Phyllostomidae (Chiroptera). Syst. Zool. 26: GREENBAUM, I. F., R. J. BAKER, AND D. E. WIL- SON Evolutionary implications of the karyotype of the stenodermine genera Ardops, Ariteus, Phyllops and Ectophylla. Bull. Southern Calif. Acad. Sci. 74: HECHT, M. K., AND J. L. EDWARDS The determination of parallel or monophyletic relationships: the proteid salamanders-a test case. Amer. Natur. 110: MILLER, G. S., JR The families and genera of bats. Bull. U.S. Nat. Mus. 57:xvii p. PATTON, J. C Evolutionary implications of the G-banded and C-handed karyotypes of phyllostomatoid bats. Masters' thesis, Texas Tech Univ. vi + 59 p. SMITH, J. D Chiropteran evolution, p In R. J. Baker, J. K. Jones, Jr., and D. C. Carter (eds.), Biology of Bats of the New World Family Phyllostomatidae, Part I. Spec. Puhl. Mus., Texas Tech Univ. 10:l-218. STOCK, A. D Chromosome banding pattern homology and its phylogenetic implications in the bat genera Carollia and Choeroniscus. Cytog. and Cell Genet. 14:34-41.