The demography of Howler Monkeys (Alouatta palliata) on Barro Colorado Island,Panamá

Chronological ages of Alouattaon Barro Colorado Island (BCI) were estimated from longitudinal dental wear. Combining these data with visual censuses, we approximated the study population’s age profile. A stable model was then constructed; from it we derived agespecific mortality rates. Mortality of immature animals is high, with 88% of the males and 65% of the females dying before 5 years. Adult mortality is low until 11 years, when it accelerates. The average adult life span is 16.6 years for males and 15.5 for females. The maximum life span is over 20 years. A pubertal male growth spurt occurs from 3 to 5 years, at which time females are primiparous. Sexual size differences develop primarily during this time. The 1976 age profile had anomalously few animals aged 7 years and males aged 8–9 and 15–16 years. With corroborating evidence, we hypothesize that these deficits resulted from excessive rainfall in 1963 and 1971, which reduced the fall fruit crop and led to a high juvenile mortality. Within half of our study troops, some adult males have nearly identical ages, suggesting an active process of agemate coalition. We hypothesize a form of kin selection, wherein peripheral male cohorts from the same natal troop have greater survival and social success than solitary animals. The stable model suggests an annual growth rate of 1.5% during the 1970s. Estimates of 16.7 and 4% for the previous two decades, following a yellow-fever epidemic, imply that the BCI population is becoming stationary. A very different age structure existed on neighboring Orchid Island in 1976, suggesting general food limitation. By contrast, the lowered, but continuing growth on BCI suggests a less drastic limiting mechanism. We hypothesize that intratroop social competition limits population growth by regulating subadult survival rates during food scarcity cycles.     

Anatomy of the squirrel wrist: bones, ligaments, and muscles

Anatomical differences among squirrels are usually most evident in the comparison of flying squirrels and nongliding squirrels. This is true of wrist anatomy, probably reflecting the specializations of flying squirrels for the extension of the wing tip and control of it during gliding. In the proximal row of carpals of most squirrels, the pisiform articulates only with the triquetrum, but in flying squirrels there is also a prominent articulation between the pisiform and the scapholunate, providing a more stable base for the styliform cartilage, which supports the wing tip. In the proximal wrist joint, between these carpals and the radius and ulna, differences in curvature of articular surfaces and in the location of ligaments also correlate with differences in degree and kind of movement occurring at this joint, principally reflecting the extreme dorsal flexion and radial deviation of the wrist in flying squirrels when gliding. The distal wrist joint, between the proximal and distal rows of carpals, also shows most variation among flying squirrels, principally in the articulations of the centrale with the other carpal bones, probably causing the distal row of carpal bones to function more like a single unit in some animals. There is little variation in wrist musculature, suggesting only minor evolutionary modification since the tribal radiation of squirrels, probably in the early Oligocene. Variation in the carpal bones, particularly the articulation of the pisiform with the triquetrum and the scapholunate, suggests a different suprageneric grouping of flying squirrels than previously proposed by McKenna (1962) and Mein (1970). J. Morphol. 246:85-102, 2000. Published 2000 Wiley-Liss, Inc.     

Amazonian biodiversity: assessing conservation priorities with taxonomic data

Data from 3991 records of museum collections representing 421 species of plants, arthropods, amphibians, fish, and primates were analyzed with GIS to identify areas of high species diversity and endemism in Amazonia. Of the 472 1 × 1° grid cells in Amazonia, only nine cells are included in the highest species diversity category (43–67 total species) and nine in the highest endemic species diversity category (4–13 endemic species). Over one quarter of the grid cells have no museum records of any of the organisms in our study. Little correspondence exists between the centers of species diversity identified by our collections-based data and those areas recommended for conservation in an earlier qualitative study of Amazonian biodiversity. Museum collections can play a vital role in identifying species-rich areas for potential conservation in Amazonia, but a concerted and structured effort to increase the number and distribution of collections is needed to take maximum advantage of the information they contain.     

Taxonomic status of Saguinus tripartitus (Milne-Edwards, 1878)

A review of specimens and field notes of Carlos Olalla and his sons showed that they collected Saguinus tripartitus and Saguinus fuscicollis lagonotus at the same place on the right bank of the lower Rio Napo in Peru. Thus, these two forms are sympatric, although they probably occur in different habitats. Therefore, Saguinus tripartitus should be treated as a distinct species, not as a subspecies of Saguinus fuscicollis.     

Two aeromonads: Growth of symbionts fromHydra viridis

A large population of bacteria resides in the gastrodermal and ovarian tissue of the freshwater green coelenterateHydra viridis (Ohio, Jubilee, and Carolina strains). The intracellular bacteria are strongly correlated with the presence of symbiotic chlorellae in the animal cells. The bacteria accompany the chlorellae when they are expelled in vesicles during stages of sexual maturation. Two isolates of these bacteria were taken from ruptured bacterial-algal vesicles flushed out of the enteron of surface-sterilzed hydras. They were cultured on proteose peptone. Both were identified asAeromonas punctata, on the basis of over forty traits. These large, Gram-negative rods differ very little from published characteristics ofA. punctata subsp.punctata. UnlikeA. punctata subsp.punctata, the hydra symbionts grew on KCN broth and lacked the lysine decarboxylase reaction. We identified the two isolates as members of the same new strain ofAeromonas punctata symbiotic inHydra viridis. A different aeromonad could not be isolated from vesicles flushed out of surface-sterilized hydras, but it appeared along with the first aeromonad on plates from which smears of the holdfast and hypostome region of ethanol-rinsed hydra were made. This second orange-pigmented bacterium in a member of the holdfast microbial community associated with hydra and hydra eggs. It differed fromAeromonas hydrophila subsp.anaerogenes in only 5 out of over 40 traits tested. All differences were losses of metabolic activities. Both hydra-associatedA. hydrophila andA. punctata, which are easily grown, and yet form regular and natural associations with the greenHydra viridis, may prove useful for understanding metabolic relationships in micro-organisms adapted for symbiotic associations.     

Predation rate on artificial nests increases with human housing density in suburban habitats

Predation causes most nest failure in birds. Predator communities are likely to vary across a gradient of increasing urbanization, so nest predation also is likely to vary across this gradient. Although predation is thought to decline with increasing urbanization, relatively little is known about variation in predation pressure within strata along an urban gradient and how factors known to affect nest success, such as nest location, interact with urban variables, such as human housing density. Native habitats are frequently fragmented and isolated by suburban residential development, thus we quantified predation rates on artificial nests located in natural oak scrub patches within a suburban matrix in south-central Florida. We examined patterns of predation based on nest location relative to habitat edges, artificial nest weathering treatment, nest shrub height, and human housing density. Over two 18-d trials, we placed a total of 240 nests, each containing a single quail egg and a clay sham, along three roadside transects. Nest predation was not influenced by proximity to edge, nest weathering, or trial date, but was highest at high housing density and lowest at low housing density. The proportion of quail eggs removed from nests increased with human housing density. Birds were the most frequent predators of artificial nests, but the relative frequency of predation by birds or mammals did not differ relative to any of our treatments. Higher rates of nest predation with increasing human housing density within suburban habitats may reflect changes in habitat structure and composition that increase the vulnerability of nests to predation or changes in the composition of the predator community. Our results modify the conclusions of previous studies by suggesting that at scales smaller than the entire urban gradient, nest predation may increase with human housing density, one common measure of urbanization.     

Cognitive and psychomotor responses to high-altitude exposure in sea level and high-altitude residents of Ecuador

Background

High-altitude inhabitants have cardiovascular and respiratory adaptations that are advantageous for high-altitude living, but they may have impaired cognitive function. This study evaluated the influence of altitude of residence on cognitive and psychomotor function upon acute exposure to very high altitude.

Findings

Ecuadorians (31 residing at 0–1,500 m [LOW], 78 from 1,501–3,000 m [MOD], and 23 living >3,000 m [HIGH]) were tested upon their arrival to a hut at 4,860 m on Mount Chimborazo. Cognitive/psychomotor measurements included a go-no-go test (responding to a non-visual stimulus), a verbal fluency test (verbalizing a series of words specific to a particular category), and a hand movement test (rapidly repeating a series of hand positions). Mean differences between the three altitude groups on these cognitive/psychomotor tests were evaluated with one-way ANOVA. There were no significant differences (p = 0.168) between LOW, MOD, and HIGH for the verbal fluency test. However, the go-no-go test was significantly lower (p < 0.001) in the HIGH group (8.8 ± 1.40 correct responses) than the LOW (9.8 ± 0.61) or MOD (9.8 ± 0.55) groups, and both MOD (97.9 ± 31.2) and HIGH (83.5 ± 26.7) groups completed fewer correct hand movements than the LOW (136.6 ± 37.9) subjects (p < 0.001).

Conclusions

Based on this field study, high-altitude residents appear to have some impaired cognitive function suggesting the possibility of maladaptation to long-term exposure to hypobaric hypoxia.     

Evolutionary acceleration in the most endangered mammal of Canada: speciation and divergence in the Vancouver Island marmot (Rodentia, Sciuridae)

The Vancouver Island marmot is the most endangered mammal of Canada. Factors which have brought this population to the verge of extinction have not yet been fully elucidated, but the effects of deforestation and habitat fragmentation on survival rates, as well as those of variation in rainfall, temperature, snowpack depth and snowmelt strongly suggest that marmots on the island are struggling to keep pace with environmental changes. Genetic analyses, however, seem to indicate that the Vancouver Island marmot may merely represent a melanistic population of its parental species on the mainland. Were it not for its black pelage colour, it is unlikely that it would have attracted much attention as a conservation priority. Our study uses three-dimensional coordinates of cranial landmarks to further assess phenotypic differentiation of the Vancouver Island marmot. A pattern of strong interspecific divergence and low intraspecific variation was found which is consistent with aspects of drift-driven models of speciation. However, the magnitude of shape differences relative to the putatively neutral substitutions in synonymous sites of cytochrome b is too large for being compatible with a simple neutral model. A combination of bottlenecks and selective pressures due to natural and human-induced changes in the environment may offer a parsimonious explanation for the large phenotypic differentiation observed in the species. Our study exemplifies the usefulness of a multidisciplinary approach to the study of biological diversity for a better understanding of evolutionary models and to discover aspects of diversity that may be undetected by using only a few genetic markers to characterize population divergence and uniqueness.     

Carpal development and morphology in archontan mammals

Carpal morphology and development in bats, colugos, tree shrews, murids, and sciurids were studied in order to homologize carpal elements. Prenatal coalescence of discrete cartilaginous templates with a loss of a center of ossification appears to be the most common method of reducing carpal elements in these mammals. Only bats and colugos showed postnatal ossification between discrete elements as a method of reducing carpal elements. Carpal morphology of tree shrews is more diverse than previously reported. Ptilocercus shows a highly derived carpal morphology that may be related to its relatively greater arboreality. Dendrogale exhibits what is most likely the ancestral tupaiid carpal morphology. Carpal morphologies of Tupaia, Urogale, and Anathana are identical to each other. Carpal morphology differs between megachiropterans and microchiropterans. These differences may be related to different aerodynamic constraints between the suborders. The carpal morphology of microchiropterans is diverse and may reflect different adaptive regimes between microchiropteran families. Carpal morphology of the colugos shows both megachiropteran and microchiropteran characters. The function of these characters in colugos and bats (stabilization of the carpus in dorsiflexion) is proposed to be similar, although the locomotor roles may be quite different between these taxa. J. Morphol. 235:135–155, 1998. © 1998 Wiley-Liss, Inc.     

Comparative myology of the forelimb of squirrels (Sciuridae)

The musculature of the shoulder, arm, and forearm was studied in 19 genera of squirrels, representing the Pteromyinae (flying squirrels) and all 7 tribes of the Sciurinae (tree and ground squirrels). The objective was to locate derived anatomical features of functional or phylogenetic significance and to determine how much morphological variation underlies the diverse locomotor behavior of squirrels, which includes terrestrial and arboreal bounding, climbing, digging, and gliding. The fossil evidence suggests that arboreality is primitive for squirrels, and in fact tree squirrels appear to represent the primitive sciurid morphology. Ground squirrels are less uniform and exhibit a few derived features, including a clavobrachialis muscle not seen in other squirrels. Pygmy tree squirrels, which have evolved independently in three tribes, exhibit convergence of forelimb anatomy, including the loss or reduction of several muscles in the shoulder and forearm. The forelimb anatomy of flying squirrels is the most derived and differs from that of tree squirrels in details of shoulder, arm, and forearm musculature. Some of these muscular differences among squirrels have phylogenetic significance, being shared by closely related genera, but none has significance above the tribal level. Many of the differences suggest a variety of changes in function that are amenable to further study. J. Morphol. 234:155–182, 1997. © 1997 Wiley-Liss, Inc.