Resampling-based approaches to study variation in morphological modularity

Modularity has been suggested to be connected to evolvability because a higher degree of independence among parts allows them to evolve as separate units. Recently, the Escoufier RV coefficient has been proposed as a measure of the degree of integration between modules in multivariate morphometric datasets. However, it has been shown, using randomly simulated datasets, that the value of the RV coefficient depends on sample size. Also, so far there is no statistical test for the difference in the RV coefficient between a priori defined groups of observations. Here, we (1), using a rarefaction analysis, show that the value of the RV coefficient depends on sample size also in real geometric morphometric datasets; (2) propose a permutation procedure to test for the difference in the RV coefficient between a priori defined groups of observations; (3) show, through simulations, that such a permutation procedure has an appropriate Type I error; (4) suggest that a rarefaction procedure could be used to obtain sample-size-corrected values of the RV coefficient; and (5) propose a nearest-neighbor procedure that could be used when studying the variation of modularity in geographic space. The approaches outlined here, readily extendable to non-morphometric datasets, allow study of the variation in the degree of integration between a priori defined modules. A Java application – that will allow performance of the proposed test using a software with graphical user interface – has also been developed and is available at the Morphometrics at Stony Brook Web page (http://life.bio.sunysb.edu/morph/).

Levels and probable origin of predatory scarring on humpback whales (Megaptera novaeangliae) in east Australian waters

To investigate the incidence of non-lethal predation in Southern Hemisphere whales, more than 3400 fluke-identification photographs from resight histories of 1436 east Australian humpback whales were examined for evidence of predatory markings. Photographs were obtained from 1984 to 1996 at various locations along the east coast of Australia, from northern Queensland to southern New South Wales. Photographs were classified in terms of the level and type of scarring. The possible predator and whether the markings appeared fresh were also noted. In all, 17% of identified east Australian humpbacks possessed some form of predatory scarring, 57% of which was minor and 43% major. Almost all predatory scarring was consistent with that inflicted by killer whales. Only three whales demonstrated an increase in the level of predatory scarring after their first sightings. Two incidents of fresh scarring were recorded, and one fatal killer whale attack on a humpback whale calf was directly observed. The overall level of predatory scarring found in this study is comparable to those found in studies for Northern Hemisphere humpback whales. The low incidence of adult whales showing their first sign of predatory scarring after their initial sighting, and the small number possessing recent scarring, support the idea that east Australian humpback whales experience most predatory attacks early in life.

Degenerate dentition of the dugong (Dugong dugon), or why a grazer does not need teeth: morphology, occlusion and wear of mouthparts

The morphology and functional occlusion of the cheekteeth of 57 dugongs Dugong dugon of both sexes were examined using reflected light and scanning electron microscopy, radiography, hardness testing and skull manipulation. The functional morphology of the horny oral pads was also described. Mouthparts and body size allometry was examined for ontogenetic and gender-related trends. We found that the worn erupted cheekteeth of the dugong are simple flat pegs composed of soft degenerative dentine. During occlusion, the mandible moves in a mainly antero-lingual direction, with the possibility of mandibular retraction in some individuals. Anterior parts of the cheektooth row may become non-functional as a dugong ages. As a function of body size, dugong cheekteeth are extremely small compared with those of other mammalian herbivores, and with other hindgut fermenters in particular. The morphology, small size and occlusal variability of the cheekteeth suggest that there has not been strong selective pressure acting to maintain an effective dentition. In contrast, great development of the horny pads and associated skull parameters and their lower size variability suggest that the horny pads may have assumed the major role in food comminution.

Learning of foraging skills by fish

This chapter outlines the relationships between a number of key factors that influence learning and memory, and illustrates them by reference to studies on the foraging behaviour of fish. Learning can lead to significant improvements in foraging performance in only a few exposures, and at least some fish species are capable of adjusting their foraging strategy as patterns of patch profitability change. There is also evidence that the memory window for prey varies between fish species, and that this may be a function of environmental predictability. Convergence between behavioural ecology and comparative psychology offers promise in terms of developing more mechanistically realistic foraging models and explaining apparently 'suboptimal' patterns of behaviour. Foraging decisions involve the interplay between several distinct systems of learning and memory, including those that relate to habitat, food patches, prey types, conspecifics and predators. Fish biologists, therefore, face an interesting challenge in developing integrated accounts of fish foraging that explain how cognitive sophistication can help individual animals to deal with the complexity of the ecological context.

Physiological thermoregulation in a crustacean? Heart rate hysteresis in the freshwater crayfish Cherax destructor

Differential heart rates during heating and cooling (heart rate hysteresis) are an important thermoregulatory mechanism in ectothermic reptiles. We speculate that heart rate hysteresis has evolved alongside vascularisation, and to determine whether this phenomenon occurs in a lineage with vascularised circulatory systems that is phylogenetically distant from reptiles, we measured the response of heart rate to convective heat transfer in the Australian freshwater crayfish, Cherax destructor. Heart rate during convective heating (from 20 to 30 degreesC) was significantly faster than during cooling for any given body temperature. Heart rate declined rapidly immediately following the removal of the heat source, despite only negligible losses in body temperature. This heart rate 'hysteresis' is similar to the pattern reported in many reptiles and, by varying peripheral blood flow, it is presumed to confer thermoregulatory benefits particularly given the thermal sensitivity of many physiological rate functions in crustaceans. (C) 2004 Published by Elsevier Inc.

Temperature-dependent sex ratio in a bird

To our knowledge, there is, so far, no evidence that incubation temperature can affect sex ratios in birds, although this is common in reptiles. Here, we show that incubation temperature does affect sex ratios in megapodes, which are exceptional among birds because they use environmental heat sources for incubation. In the Australian brush-turkey Alectura lathami, a mound-building megapode, more males hatch at low incubation temperatures and more females hatch at high temperatures, whereas the proportion is 1 : 1 at the average temperature found in natural mounds. Chicks from lower temperatures weigh less, which probably affects offspring survival, but are not smaller. Megapodes possess heteromorphic sex chromosomes like other birds, which eliminates temperature-dependent sex determination, as described for reptiles, as the mechanism behind the skewed sex ratios at high and low temperatures. Instead, our data suggest a sex-biased temperature-sensitive embryo mortality because mortality was greater at the lower and higher temperatures, and minimal at the middle temperature where the sex ratio was 1 : 1.

Locomotion and gaits of the northern brown bandicoot, Isoodon macrourus (Marsupalia: Peramelidae)

Gait repertoires of the northern brown bandicoot, Isoodon macrourus, were studied over a wide range of locomotor speeds. At low relative speeds, bandicoots used symmetrical gaits that included pacing, trotting, and lateral sequence strides. Forefoot contact duration was generally shorter than hind foot contact duration at all speeds. At moderate relative speeds bandicoots used half-bounding gaits with either no period of suspension or with a short gathered suspension. At high speeds the predominant gait had both a short extended and a short gathered suspension, although some strides comprised only an extended suspension. Increases in speed were accompanied by increases in spinal extension, presumably leading to the extended suspensions. On a stationary treadmill individuals occasionally used a bipedal gait. Maximum half-bounding speeds appear to be relatively low in this species.

Freshwater to seawater acclimation of juvenile bull sharks ( Carcharhinus leucas): plasma osmolytes and Na +/K +-ATPase activity in gill, rectal gland, kidney and intestine

This study examined the osmoregulatory status of the euryhaline elasmobranch Carcharhinus leucas acclimated to freshwater (FW) and seawater ( SW). Juvenile C. leucas captured in FW ( 3 mOsm l(-1) kg(-1)) were acclimated to SW ( 980 - 1,000 mOsm l(-1) kg(-1)) over 16 days. A FW group was maintained in captivity over a similar time period. In FW, bull sharks were hyper-osmotic regulators, having a plasma osmolarity of 595 mOsm l(-1) kg(-1). In SW, bull sharks had significantly higher plasma osmolarities ( 940 mOsm l(-1) kg(-1)) than FW-acclimated animals and were slightly hypoosmotic to the environment. Plasma Na+, Cl-, K+, Mg2+, Ca2+, urea and trimethylamine oxide (TMAO) concentrations were all significantly higher in bull sharks acclimated to SW, with urea and TMAO showing the greatest increase. Gill, rectal gland, kidney and intestinal tissue were taken from animals acclimated to FW and SW and analysed for maximal Na+/ K+-ATPase activity. Na+/ K+-ATPase activity in the gills and intestine was less than 1 mmol Pi mg(-1) protein h(-1) and there was no difference in activity between FW- and SW-acclimated animals. In contrast Na+/ K+-ATPase activity in the rectal gland and kidney were significantly higher than gill and intestine and showed significant differences between the FW- and SW-acclimated groups. In FW and SW, rectal gland Na+/ K+-ATPase activity was 5.6 +/- 0.8 and 9.2 +/- 0.6 mmol Pi mg(-1) protein h(-1), respectively. Na+/ K+-ATPase activity in the kidney of FW and SW acclimated animals was 8.4 +/- 1.1 and 3.3 +/- 1.1 Pi mg(-1) protein h(-1), respectively. Thus juvenile bull sharks have the osmoregulatory plasticity to acclimate to SW; their preference for the upper reaches of rivers where salinity is low is therefore likely to be for predator avoidance and/or increased food abundance rather than because of a physiological constraint.

Diving behaviour of a reptile (Crocodylus johnstoni) in the wild: Interactions with heart rate and body temperature

The differences in physical properties of air and water pose unique behavioural and physiological demands on semiaquatic animals. The aim of this study was to describe the diving behaviour of the freshwater crocodile Crocodylus johnstoni in the wild and to assess the relationships between diving, body temperature, and heart rate. Time-depth recorders, temperature-sensitive radio transmitters, and heart rate transmitters were deployed on each of six C. johnstoni (4.0-26.5 kg), and data were obtained from five animals. Crocodiles showed the greatest diving activity in the morning (0600-1200 hours) and were least active at night, remaining at the water surface. Surprisingly, activity pattern was asynchronous with thermoregulation, and activity was correlated to light rather than to body temperature. Nonetheless, crocodiles thermoregulated and showed a typical heart rate hysteresis pattern (heart rate during heating greater than heart rate during cooling) in response to heating and cooling. Additionally, dive length decreased with increasing body temperature. Maximum diving length was 119.6 min, but the greatest proportion of diving time was spent on relatively short (

Molecular analysis reveals tighter social regulation of immigration in patrilocal populations than in matrilocal populations

Human social organization can deeply affect levels of genetic diversity. This fact implies that genetic information can be used to study social structures, which is the basis of ethnogenetics. Recently, methods have been developed to extract this information from genetic data gathered from subdivided populations that have gone through recent spatial expansions, which is typical of most human populations. Here, we perform a Bayesian analysis of mitochondrial and Y chromosome diversity in three matrilocal and three patrilocal groups from northern Thailand to infer the number of males and females arriving in these populations each generation and to estimate the age of their range expansion. We find that the number of male immigrants is 8 times smaller in patrilocal populations than in matrilocal populations, whereas women move 2.5 times more in patrilocal populations than in matrilocal populations. In addition to providing genetic quantification of sex-specific dispersal rates in human populations, we show that although men and women are exchanged at a similar rate between matrilocal populations, there are far fewer men than women moving into patrilocal populations. This finding is compatible with the hypothesis that men are strictly controlling male immigration and promoting female immigration in patrilocal populations and that immigration is much less regulated in matrilocal populations.