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The G- and C-banded chromosomes of six species of hare (genus Lepus) are presented and compared. No variation in gross chromosome morphology or banding pattern was observed indicating that speciation in this widespread genus has not involved karyotypic change.
The chromosome banding patterns of the domestic rabbit, Oryctolagus cuniculus, the brush rabbit, Sylvilagus bachmani, and the snowshoe hare, Lepus americanus, are nearly identical except for minor differences in the amount of constitutive heterochromatin present. The major mechanisms of chromosome evolution in leporid lagomorphs are centric fusion and addition of heterochromatin. The G- and C-banding patterns of the pika, Ochotona princeps, revealed little easily recognized structural homology with the leporid species. Several tentative banding pattern matches were found for segments of some chromosomes of Ochotona, indicating that tandem fusions may have been responsible for structural modification of the early lagomorph genome. Chromosome evolution in the lagomorphs and the use of chromosomal data in studies of mammalian systematics are discussed.
Chromosome banding patterns of Lepus saxatilis, 2n = 48, and Pronolagus rupestris, 2n = 42, are presented. Comparison of G-banded karyotypes allows the identification of similar elements in both species. The karyotype of P. rupestris differs from that of L. saxatilis by the presence of three fusions in the former. Comparative studies with the fusion products of Oryctolagus cuniculus indicate that fusion and not fission is the major factor in chromosomal evolution of these leporids. The chromosomal conservatism of the hares is compared to the karyotypic variability of the rabbits and possible causes are discussed.
The banding patterns of mitotic chromosome from three cottontail species, Sylvilagus aquaticus (2n = 38), S. floridanus (2n = 42), and S. transitionalis (2n = 46), are presented and compared with those of the proposed leporid ancestral karyotype, the latter being reflected in a species of hare, Lepus saxatilis (2n = 48). The differences in the diploid numbers of the cottontail species are primarily due to the fixation of Robertsonian fusions which have occurred during the evolution of their respective genomes. Of the eight fusion products identified, seven were species specific, while one, which is thought to reflect their more recent common ancestory, is shared by both S. aquaticus and S. floridanus. Other karyotypic differences include interspecific variation in the amount and distribution of constitutive heterochromatin, as well as the presence of two autosomal pairs in S. transitionalis which do not have apparent banding homologies either with the chromosomes of other cottontails or with those of the Lepus genome. The tendency for certain chromosomes in the ancestral karyotype to show a predisposition to undergo fusion events within the Leporidae is discussed.
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The genus Sylvilagus, which comprises the New World cottontail rabbits, contains several commercially important as well as endangered (or threatened) species. Understanding the evolution of this group is pertinent to their management and conservation. The purpose of this study was to examine the evolutionary history of the cottontails using sequence data from the mitochondrial 12S rRNA gene. The 12S data provide a robust phylogeny which was supported under a variety of phylogenetic approaches and transition/transversion (Ti/Tv) weighting schemes. Stem and loop regions of the gene were analyzed separately and two different methods of estimating Ti/Tv ratios were employed. The phylogeny obtained was consistent with available cytogenetic information. The 12S data indicate that separate generic status for the pygmy rabbit, Brachylagus idahoensis, is warranted based on its phylogenetic position and sequence divergence values. Additionally, the taxa which are geographically adjacent are also phylogenetically closely related; for example, the marsh rabbit, S. palustris, and the swamp rabbit, S. aquaticus, are sister taxa, as are the mountain cottontail, S. nuttallii, and desert cottontail, S. audubonii. This finding suggests that recent vicariance events might explain the diversification of several cottontail lineages.
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Previous studies in small mammals showed that blood-sucking bugs (Reduviidae, Heteroptera) can be used to obtain blood from veins difficult to access by human experimenters. In the present study, we validated the use of reduviid bugs for endocrinological studies in endotherms using domestic rabbits as a model organism. Two processes could alter the hormone concentrations in the blood ingested by the bug: (1) Mixing of ingested blood with saliva, gut fluid, or hemolymph and (2) digestive processes. We compared concentrations of progesterone, testosterone, and hydrocortisone in blood samples that were acquired from domestic rabbits (Oryctolagus cuniculus) by bugs (Dipetalogaster maxima) with hormone concentrations in blood obtained from the same individual rabbits with a conventional method, i.e., syringe. We found no significant differences in hormone concentrations between the two methods. Thus, the mixing effect is negligible immediately after the blood meal. In addition, we also could not find significant changes in concentrations of progesterone and hydrocortisone for up to 8h after the blood meal. Whereas levels of hydrocortisone remained unchanged for even 24h, progesterone levels significantly increased between eight and 24h. Thus, the bugs' excretory apparatus did not fractionate between water and hormones. Thirdly, we hypothesized that reduviid bugs impose less stress on the rabbits than the conventional method. We showed that deviations in hydrocortisone concentrations between the two blood sampling routines were lower when the bug method was used first and higher when the conventional method was used first. Thus, bugs imposed less stress on the study animals than the conventional method. Overall, we conclude that reduviid bugs present a minimally invasive method for obtaining blood from endotherm animals for endocrinological studies.
Geographical genetic population structure was determined for an endemic African leporid, Smith's red rock rabbit, Pronolagus rupestris. Restriction fragment length polymorphism analysis of mitochondrial DNA from 55 specimens revealed 32 distinct material lineages for the population sampled. The data show two major genetic assemblages separated by a mean sequence divergence of 7.94 per cent (+/- 1.40 per cent) and provide little support for the continued recognition of most of the described subspecies. The south-eastern assemblage is confined to the mountain ranges comprising the Great Escarpment of South Africa, while the north-western assemblage is not so tightly constrained. With the possible exception of elevation, no readily apparent ecological or topographical barrier could be identified which delimits the two mitochondrial clades. The sequence divergence separating the south-eastern and north western P. rupestris clades is high, and approximates the interspecific sequence divergences detected between P. rupestris and other Pronolagus species. The two P. rupestris clades are parapatric for part of their distribution, and the absence of shared mtDNA lineages is consistent with the hypothesis that the two populations are reproductively isolated from each other. We provisionally interpret this to reflect the presence of two hitherto undetected biological species in what has conventionally been recognized as a single taxon, P. rupestris.
Cercopithifilaria leporinus n. sp. from the subcutaneous tissues of the trunk of snowshoe hares (Lepus americanus Erxleben) in Ontario and Alberta, Canada, is described. This is the only species of Dipetalonema--like filarioid known from lagomorphs. It is distinguished from other species of Cercopithifilaria by its small size, numerous mucrons on the female tail, vulva leading into a large, spherical vestibule and the pattern of papillae on the male tail. Eight species of filarioids, representing four genera, are now known from lagomorphs. Dirofilaria timidi Gubanov and Fedorov, 1966 is considered as a species inquirenda.
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Phylogeographical investigations of arctic organisms provide spatial and temporal frameworks for interpreting the role of climate change on biotic diversity in high-latitude ecosystems. Phylogenetic analyses were conducted on 473 base pairs of the mitochondrial control region in 192 arctic hares (Lepus arcticus, Lepus othus, Lepus timidus) and two individual Lepus townsendii. The three arctic hare species are closely related. All L. othus individuals form one well-supported clade, L. arcticus individuals form two well-supported clades, and L. timidus individuals are scattered throughout the phylogeny. Arctic hare distribution was altered dramatically following post-Pleistocene recession of continental ice sheets. We tested for genetic signatures of population expansion for hare populations now found in deglaciated areas. Historical demographic estimates for 12 arctic hare populations from throughout their range indicate that L. arcticus and L. othus persisted in two separate North American arctic refugia (Beringia and High Canadian Arctic) during glacial advances of the Pleistocene, while the high genetic diversity in L. timidus likely reflects multiple Eurasian refugia.
Fluorescence in situ hybridization (FISH) was used to define homologous segments among representatives of 7 of the 11 recognized leporid genera. Chromosome painting using 22 rabbit chromosome-specific paints derived from flow-sorted chromosomes revealed that at least 18 fusions and six fissions differentiate the extant karyotypes from the presumed ancestral state (2n = 48). The riverine rabbit, Bunolagus monticularis, has the most derived karyotype, differing from the ancestor by seven fusions and five fissions, followed by Pronolagus rupestris, with four fusions and one fission. These findings are consistent with the proposed Palaeolaginae/Leporinae dichotomy in the lagomorphs. The molecular cytogenetic data allow for a refinement of the structural changes that have shaped genome evolution in this group of mammals and underscore the rapid radiation of the Leporidae suggested by mitochondrial DNA sequence data.
Chromosomes from cultured fibroblasts of four cottontail species (Sylvilagus audubonii, 2n = 42; S. idahoensis, 2n = 44; S. nuttallii, 2n = 42; and S. palustris, 2n = 38) were analyzed using G- and C-banding techniques. The evolutionary restructuring of the genomes of these species was traced by comparing their banded chromosomes to those of Lepus saxatilis, a species of hare in which the leporid ancestral karyotype is thought to have been conserved. Chromosomal evolution appears to have proceeded primarily through changes in the amount and distribution of heterochromatin and through fixation of Robertsonian fusions. Excluding heterochromatic differences, S. audubonii and S. nuttallii are karyotypically very similar, as are S. aquaticus and S. palustris (previously reported). The genome of the taxonomically controversial species S. idahoensis, compared to other cottontail species, is markedly impoverished in C-band material. These data and those of cottontail species previously described in the literature are incorporated in two alternative phylogenetic schemes.