Browsing by Author "Layne, James Nathaniel."
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Item Comparative morphology of spermatozoa of the rodent genus Peromyscus (Muridae). American Museum novitates ; no. 2532(New York, N.Y. : American Museum of Natural History, 1974) Linzey, Alicia V.; Layne, James Nathaniel."The morphology of spermatozoa of 27 species and seven subgenera of the genus Peromyscus was studied. Measurements of length and width of the head, midpiece length, and tail length of the sperm of 25 species are given. Two major sperm types occur in the series. Sperm of two species of the subgenus Habromys examined have large heads lacking the hooklike process characteristic of many murid rodents, whereas all other species studied have sperm with hooked heads. Although there are species differences in shape of the head and of various measurements of the sperm among the group with hooked heads, no definite patterns of variation corresponding to presently recognized subgenera or to the species groups within the subgenus Peromyscus were seen. There is no obvious correlation between body size and sperm size"--P. [1].Item Comparative morphology of the male reproductive tract in the rodent genus Peromyscus (Muridae). American Museum novitates ; no. 2355(New York, N.Y. : American Museum of Natural History, 1969) Linzey, Alicia V.; Layne, James Nathaniel."The male genital tracts of 28 species of Peromyscus were examined. On the basis of the accessory glands and other structures seven major groups can be distinguished within the genus. These correspond to the subgenera of Hooper and Musser (1964). The subgenus Haplomylomys possesses a full complement of accessory glands, including ampullary, vesicular, anterior prostate, dorsal prostate, ventral prostate, (two pairs), bulbo-urethral, and preputial glands. The subgenus Peromyscus differs only in lacking functional preputials, although these glands are present in rudimentary condition in some species. Megadontomys and Isthmomys are fundamentally similar to Peromyscus, although differing from that group and each other in numbers, proportional size, or morphology of certain glands. Isthmomys may diverge more from peromyscus than Megadontomys. The remaining three groups are markedly different from other species in genital morphology. Osgoodomys lacks vesicular and both anterior and dorsal prostate glands but has exceptionally large and distinctive ampullaries and well-developed preputials. Podomys and Habromys share the condition of greatly reduced vesiculars and anterior and dorsal prostates but differ in other features. Podomys has enlarged ampullaries and a deferent duct of unique structure, whereas Habromys has normal ampullaries and a typical derent duct but greatly enlarged ventral prostates. At least some of the species groups of the subgenus Peromyscus appear to be characterized by common genital features. These were more subtle than the difference betwen major groups and will require further study for verification. The genital data can be reconciled with the view that the genus Peromyscus is a natural assemblage of species in which some forms have diverged greatly, but they can be interpreted in support of the hypothesis that the genus is prophyletic. In either case, the present subgenera Osgoodomys, Podomys, and habromys may warrant exclusion from the genus on the basis of their extremely divergent reproductive morphology"--P. 45.Item Digging behavior of four species of deer mice (Peromyscus). American Museum novitates ; no. 2429(New York, N.Y. : American Museum of Natural History, 1970) Layne, James Nathaniel.; Ehrhart, Llewellyn M."Certain aspects of digging behavior in four species of deer mice, Peromyscus (P. floridanus, P. gossypinus, P. leucopus, and P. polionotus), were studied to determine the relationships between the level of digging activity and ecological factors and the possible adaptive significance of such correlations. Two populations of each of three of the species (floridanus, gossypinus, and polionotus) were included to provide some indication of the magnitude of intraspecific variation in digging activity, and both field and first generation laboratory-raised subjects of the same species were studied in an attempt to distinguish between the relative influences of genetic and environmental factors on this behavior. Mice were placed individually into an open-field box containing either sand or peat and observed for a five-minute period. In addition to descriptive notes on digging behavior, number of bouts, total time spent digging, and latency (time elapsed between introduction to the apparatus and beginning of first digging bout) were recorded. Peromyscus floridanus dug relatively slowly, using the forefeet for excavating and moving material beneath the body and also to propel the substrate to the rear. In contrast to the other species, the hind feet were rarely used to kick accumulated material backward. Peromyscus gossypinus moved the forefeet more rapidly in excavating material than did floridanus and generally used the hind limbs to throw the substrate behind the body. Details of digging in leucopus were not clearly observed; but it appears to resemble gossypinus in its style of digging. Peromyscus polionotus appeared to be the most efficient digger of the four species. It moved its forefeet more rapidly than the other forms, and the hind limbs were more closely integrated into the total action pattern. Quantitatively, floridanus dug less than the other species, gossypinus and leucopus were slightly more active, whereas polionotus far exceeded all other species in mean number of bouts and total time digging and had distinctly shorter latencies. The well-developed digging behavior of polionotus is correlated with burrowing habits. All species exhibited a tendency to dig more actively on sand rather than on peat, but only in leucopus and polionotus was the discrepancy pronounced. The higher level of digging of polionotus on sand may reflect selection for substrate recognition as a result of the importance of the proper type of soil for burrow construction in this species. There seems to be no obvious adaptive basis for the sand preference of leucopus. Only in polionotus were there appreciable differences between populations in digging behavior, with leucocephalus tending to do more digging than did subgriseus. This difference may reflect more intense selection for digging in the leucocephalus population as a result of more difficult burrow construction and maintenance, constant covering of food items by blowing sand, and greater use of shallow holes to avoid predation. In general, laboratory-raised stocks fell into the same relative position as field groups in the aspects of digging behavior studied, indicating a genetic basis of the differences observed. However, in all stocks except P. p. leucocephalus there was a tendency for reduced digging in laboratory-reared subjects. The differences between field and laboratory-raised groups appear to be of environmental origin, either reflecting the absence of experience on natural substrates or an effect of the homogeneous laboratory environment on other aspects of behavior, such as activity, temperament, etc., which in turn influence digging performance. The fact that laboratory-reared leucocephalus actually dug more than did field subjects may indicate either a stronger genetic basis for digging in this stock or a lesser effect of laboratory conditions, perhaps because of the relative homogeneity of the natural environment of this population compared with that of the other stocks. Differences in the present results and those of previous studies of digging behavior in Peromyscus dealing with some of the same species appear to be attributable to the types of testing apparatus and procedures utilized"--P. 14-15.Item Ecology of small mammals in a flatwoods habitat in north-central Florida, with emphasis on the cotton rat (Sigmodon hispidus). American Museum novitates ; no. 2544(New York, N.Y. : American Museum of Natural History, 1974) Layne, James Nathaniel."The small mammals of a pine flatwoods habitat in north-central Florida were studied during 1960 to 1972. Didelphis virginiana, Cryptotis parva, Oryzomys palustris, Reithrodontomys humulis, Peromyscus gossypinus, and Rattus rattus were live-trapped on the study plot. Lasiurus seminolus, Scalopus aquaticus, Sylvilagus floridanus, Procyon lotor, and Geomys pinetis were also recorded. Of the trappable species, Cryptotis, Reithrodontomys, Peromyscus, and Sigmodon were considered regular residents of the study plot, and data are given on their trappability, populations, body weight, sex ratio, reproduction, longevity, and movements. A portion of the study plot was burned in 1960, and the responses of the small mammal populations are documented. Information on mammals in various types of Florida flatwoods habitats is summarized. Data on Sigmodon hispidus from the present study and the literature are reviewed in an attempt to assess the relative influence of major climatic factors and local environmental conditions on selected ecological and life history parameters of this species. The relative importance of natality and mortality in population fluctuations of Sigmodon is also discussed"--P. 3.Item Variation in dental structures of the Florida mouse, Peromyscus floridanus. American Museum novitates ; no. 2351(New York, N.Y. : American Museum of Natural History, 1968) Wolfe, James L.; Layne, James Nathaniel."Variation in the development of the mesoloph and frequency of occurrence of the mesostyle, mesostylid, and ectostylid on the first and second molars were studied in four populations of the Florida mouse, Peromyscus floridanus. Degrees of similarity between populations based on these characters correlated well with presumed amount of gene flow between them. The molars of a population from an open woodland habitat showed a tendency toward simplification as compared with populations inhabiting dense, scrublike vegetation. No significant differences in mesoloph development ocurred in samples of two populations collected four and eight years apart"--P. 6-7.