Browsing by Subject "Oryzomys"
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Item Genetic analysis of the endangered silver rice rat (Oryzomys palustris natator) and Lower Keys marsh rabbit (Sylvilagus palustris hefneri)(Texas A&M University, 2007-04-25) Crouse, Amanda LouiseGenetic analyses of two endangered species of mammals in the Lower Keys of Florida (Lower Keys marsh rabbit, LKMR, Sylvilagus palustris hefneri; silver rice rat, SRR, Oryzomys palustris natator) were performed to evaluate the genetic structure of their populations. Mitochondrial sequence data (control region; 763 base pairs (bp), LKMR; 788 bp, SRR) were used to explore patterns of genetic variation within and among island populations in both species. Analysis of the SRR also included 8 polymorphic nuclear microsatellite loci (9 to 16 alleles). Phylogenetic analyses of mitochondrial sequence data for both species revealed two main lineages corresponding to eastern and western localities, with high levels of genetic structuring (LKMR FST = 0.982, SRR ????ST = 0.916). The two species differed in the level of sequence divergence between eastern and western populations (LKMR, 19 bp; SRR 4 bp). In addition to an overall similar pattern of genetic subdivision, populations of both species possessed low levels of mtDNA variation (haplotypic diversity in the LKMR = 66.1%, SRR = 58.6%). Microsatellite analyses of the SRR revealed subdivision between eastern and western regions. Although less pronounced than the structure observed in mtDNA, the overall pattern was still apparent. Additional examination of divergence between mainland and Lower Keys rice rats revealed a genetic division that indicated a lack of recent gene exchange between the regions (i.e. no shared haplotypes, the presence of private alleles, and distinctive separation in numerous analyses). Although this degree of division does not warrant species designation, the levels and patterns of divergence, both morphological and genetic, do suggest genetic isolation of mainland and island forms. This fact, along with restricted gene flow between the Lower Keys and the Everglades, suggests that the SRR is on an evolutionary trajectory separate from its mainland counterparts and validates its identification as a separate subspecies, Oryzomys palustris natator. Finally, the genetic division between eastern and western populations of the SRR and LKMR suggests that populations of both species in these two regions of the Lower Keys should be treated as separate management units, especially when considering the enhancement of populations via translocations.Item Population polymorphism, cladistical congruences and specific recognition of some species of Oryzomys based upon electrophoretic analyses(Texas Tech University, 1987-05) Kerridge, David CIn an attempt to better understand chromosomal polymorphisms in a population and to evaluate a systematic hypothesis developed from eladistical analyses of G-band chromosomes, an electrophoretic study was conducted on 10 species of the rodent genus Oryzomys along with seven related genera. Electrophoretic data were analyzed by cluster phenograms, Fitch-Margoliash cladograms and a Wagner cladogram. Results indicate that two species existed in a sample from Tafelberg, Suriname, consisting of 10 specimens that previously had been identified as a single species (Koop ejt. aj^., 1983). This conclusion is significant to understanding the nature and origin of chromosomal polymorphism in this sample, because nine different chromosomal polymorphisms present were among these individuals. Dividing this sample into two species partitions all chromosomal polymorphism into one species and separates them from the two individuals that were homoyzgous for all chromosomal rearrangements. Because certain eleetrophoretically identified alleles were not present in the chromosomally polymorphic population and because the other hypothetically required ancestor has not been found, I concluded that the chromosomally polymorphic population is not the result of hybridization between two chromosomally diverse taxa. A Wagner cladogram based on electrophoretic data was compared with a cladogram of relationships developed by Baker e^ al^. (1983) for chromosomal rearrangements and the two were found to be highly concordant. Additionally, to evaluate electrophoretics as a tool in faunal surveys, eight unknown specimens were included for comparison with known taxa. Possible specific designations then were assigned to these specimens on the basis of their similarity to those of certain identification. Also, some specimens from separate geographic localities were noted as potential subjects for additional research because they possibly represent different species. It was concluded that electrophoretic analysis can be a valuable tool in the primary stages of faunal surveys.Item The Lower Keys marsh rabbit and silver rice rat: steps toward recovery(Texas A&M University, 2006-10-30) Perry, Neil DesmondExtensive development has destroyed and fragmented wildlife habitat in the Lower Florida Keys. The Lower Keys marsh rabbit (LKMR; Sylvilagus palustris hefneri) and the silver rice rat (SRR; Oryzomys argentatus) are listed by the United States Fish and Wildlife Service (USFWS) and the Florida Fish and Wildlife Conservation Commission (FFWCC) as endangered species. Both species depend on coastal prairies, freshwater marshes, and intertidal salt-marsh zones. The objective of this study was to meet specific, species-level recovery goals and to add reliable information that may modify or support current recovery plans. Specifically, I (1) evaluated the use of LKMR reintroduction to suitable habitat, (2) examined characteristics of habitat used by LKMR, and (3) surveyed the Lower Florida Keys for SRRs, documenting current range and examining survey results for the past decade. I reintroduced 7 rabbits (3 males, 4 females) to suitable habitat on Water Key, and monitored their survival and release-site fidelity. All reintroduced rabbits survived and some reproduced, suggesting these translocation techniques are a viable tool for recovery. On Boca Chica Key, I radio-collared 13 LKMRs and compared vegetation characteristics between core-use and avoided areas within home ranges. Binary logistic regression associated rabbit use with high vegetation heights (7??????8 dm), low canopy coverage (<=10%), high bunchgrass densities (2.5??????3.8/sq m), and forb presence (>5%), supporting the hypothesis that LKMRs may be detrimentally impacted by hardwood encroachment into salt-marsh habitats. For LKMR recovery, I recommend management to resist hardwood encroachment, together with active predator control. I surveyed 36 locations on 18 islands for SRRs, capturing rats on 12 islands, including 2 on which SRRs had not previously been found. Comparisons of my data with historic data suggest SRRs either have increased in abundance over the past decade or that previous trapping efforts were not effective. Abundance of SRRs does not appear to be significantly different from that of populations of rice rats on the mainland. The USFWS and FFWCC should consider revising the conservation status of the SRR; however, it still should be regarded as a unique evolutionary unit with a very limited potential range.