Effect of intrahippocampal administration of anti-melanin-concentrating hormone on spatial food-seeking behavior in rats

Melanin-concentrating hormone (MCH) is a hypothalamic peptide that plays a critical role in the regulation of food intake and energy metabolism. In this study, we investigated the potential role of dense hippocampal MCH innervation in the spatially oriented food-seeking component of feeding behavior. Rats were trained for eight sessions to seek food buried in an arena using the working memory version of the food-seeking behavior (FSB) task. The testing day involved a bilateral anti-MCH injection into the hippocampal formation followed by two trials. The anti-MCH injection did not interfere with the performance during the first trial on the testing day, which was similar to the training trials. However, during the second testing trial, when no food was presented in the arena, the control subjects exhibited a dramatic increase in the latency to initiate digging. Treatment with an anti-MCH antibody did not interfere with either the food-seeking behavior or the spatial orientation of the subjects, but the increase in the latency to start digging observed in the control subjects was prevented. These results are discussed in terms of a potential MCH-mediated hippocampal role in the integration of the sensory information necessary for decision-making in the pre-ingestive component of feeding behavior.     

Convergence in tent architecture and tent-making behavior among neotropical and paleotropical bats

Fifteen species of neotropical and three species of paleotropical bats are known either to roost in or to make tents in over 80 species of vascular plants. We summarize the current knowledge of bat-tent architecture, report two new styles of tents (conical and apical) from the Paleotropics, compare the similarity in tents constructed, or used, by neotropical and paleotropical bats, and consider possible functions of tents. Seven styles of tents are known from the Neotropics, three (conical, palmate umbrella, and apical tents) are known from both the Neo- and the Paleotropics, and one (stem tent) is unique to the Paleotropics. In the Neotropics tent-roosting and/or tent-making appears to be a behavior unique to the diverse microchiropteran family Phyllostomidae (subfamily Phyllostomatinae: tribe Stenodermatini), and in the Paleotropics two members of the megachiropteran family Pteropodidae and one member of the microchiropteran family Vespertilionidae are known to construct or roost in tents. Despite the variety of plant taxa used by bats in tent construction, there appears to be a limited number of different leaf forms that can be altered by bats and used as tents. We suggest that the similarity in tent architecture observed among the neotropical and paleotropical bats is a consequence of convergence in leaf morphology among forest understory plants. The congruence in tent-making/roosting behavior observed in members of the Stenodermatini and the Pteropodidae (genusCynopterus) suggests a phylogenetic influence on these behaviors. The similarity in tent-making and/or tent-roosting behavior and life-history traits (small, <70 g, mostly foliage-roosting frugivores) among these divergent neotropical and paleotropical taxa supports a convergence hypothesis in which members of these groups have become ecological equivalents. Although actual tent-making has been observed in only one bat species to date, we suggest that the principal selective force leading to the evolution of tent-making is a polygynous mating system whereby males construct tents to gain access to females. Tents in turn provide resources that offer protection from predators and inclement weather.     

Some characteristics of spatial associative memory in the pigeon, Columba livia

Willson and Wilkie (1993) developed a novel procedure to assess pigeons' memory for the spatial location of food. Only one of four locations provided food each daily session. Each location consisted of an illuminated pecking key and grain feeder. Over different days different locations, randomly selected, provided food during a 16-min session. The pigeons tended to revisit the location at which food was found on the previous day thereby demonstrating memory for food-spatial location associations over 24 h. Three experiments were conducted to further investigate this phenomenon. In Experiment 1 the session duration was varied between 4 and 32 min. Longer sessions had no detectable effect on their ability to remember the rewarded location 24 h later, a result that suggests that only brief encounters with food at a particular location are necessary for recall. In Experiment 2 the necessity of an active search for the day's rewarded location was removed; a 5-min period in which only the rewarded key was lit preceded the regular 16-min session. Pecks to the lit key in this 5-min period produced grain on the standard schedule. This manipulation facilitated the pigeons' discovery of food but did not affect their ability to remember the rewarded location, suggesting that the process of search and discovery is not essential to the associative memory process. In Experiment 3, food was available during the complete session (non-depleting condition) or was available only during the first half of the session (depleting condition). No detectable differences in the birds' memory of yesterday's profitable location were found. This suggests that non-depletion of food is not a necessary condition for day-to-day recall of food location. Taken together these findings enlarge our understanding of the spatial associative memory process.     

Relative effects of time for speciation and tropical niche conservatism on the latitudinal diversity gradient of phyllostomid bats

Determinants of contemporary patterns of diversity, particularly those spanning extensive latitudinal gradients, are some of the most intensely debated issues in ecology. Recently, focus has shifted from a contemporary environmental perspective to a historical one in an attempt to better understand the construction of latitudinal gradients. Although the vast majority of research on historical mechanisms has focused on tropical niche conservatism (TNC), other historical scenarios could produce similar latitudinal gradients. Herein, I formalize predictions to distinguish between two such historical processes--namely time for speciation (TFS) and TNC--and test relative support based on diversity gradients of New World bats. TFS and TNC are distinctly spatial and environmental mechanisms, respectively. Nonetheless, because of the way that environmental characteristics vary spatially, these two mechanisms are hard to distinguish. Evidence provided herein suggests that TNC has had a more important effect than TFS in determining diversity gradients of New World bats. Indeed, relative effects of different historical mechanisms, as well as relative effects of historical and contemporary environmental determinants, are probably context-dependent. Future research should move away from attempting to identify the mechanism with primacy and instead attempt to understand the particular contexts in which different mechanisms have greater influence on diversity gradients.     

Non-kin cooperation in bats

Many bats are extremely social. In some cases, individuals remain together for years or even decades and engage in mutually beneficial behaviours among non-related individuals. Here, we summarize ways in which unrelated bats cooperate while roosting, foraging, feeding or caring for offspring. For each situation, we ask if cooperation involves an investment, and if so, what mechanisms might ensure a return. While some cooperative outcomes are likely a by-product of selfish behaviour as they are in many other vertebrates, we explain how cooperative investments can occur in several situations and are particularly evident in food sharing among common vampire bats (Desmodus rotundus) and alloparental care by greater spear-nosed bats (Phyllostomus hastatus). Fieldwork and experiments on vampire bats indicate that sharing blood with non-kin expands the number of possible donors beyond kin and promotes reciprocal help by strengthening long-term social bonds. Similarly, more than 25 years of recapture data and field observations of greater spear-nosed bats reveal multiple cooperative investments occurring within stable groups of non-kin. These studies illustrate how bats can serve as models for understanding how cooperation is regulated in social vertebrates.     

Predation by squirrel monkeys and double-toothed kites on tent-making bats

Central American squirrel monkeys (Saimiri oerstedi) appear to recognize the modified leaves that phyllostomid bats utilize for diurnal roost sites. The monkeys visually and manually search these bat tents for both bats and insects. Adult males are the most successful at capturing bats. Nonvolant juvenile bats are more vulnerable to monkey predation than are adults. Bats that escape monkey predation frequently are captured by doubletoothed kites (Harpagus bidentatus) that tend foraging troops of monkeys. Predation by squirrel monkeys, coupled with that of double-toothed kites, may be a significant source of mortality for tent-making bats.     

Bat fly species richness in Neotropical bats: correlations with host ecology and host brain

Patterns of ectoparasite species richness in mammals have been investigated in various terrestrial mammalian taxa such as primates, ungulates and carnivores. Several ecological or life traits of hosts are expected to explain much of the variability in species richness of parasites. In the present comparative analysis we investigate some determinants of parasite richness in bats, a large and understudied group of flying mammals, and their obligate blood-sucking ectoparasite, streblid bat flies (Diptera). We investigate the effects of host body size, geographical range, group size and roosting ecology on the species richness of bat flies in tropical areas of Venezuela and Peru, where both host and parasite diversities are high. We use the data from a major sampling effort on 138 bat species from nine families. We also investigate potential correlation between bat fly species richness and brain size (corrected for body size) in these tropical bats. We expect a relationship if there is a potential energetic trade-off between costly large brains and parasite-mediated impacts. We show that body size and roosting in cavities are positively correlated with bat fly species richness. No effects of bat range size and group size were observed. Our results also suggest an association between body mass-independent brain size and bat fly species richness. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Opposition site selection and clutch size in insects

Oviposition site selection and clutch size in parasitic insects can be viewed as problems in foraging theory. In this paper, a number of models for site selection and clutch size are developed, based on a dynamic state variable approach to optimal oviposition strategies. The models lead to predictions that are consistent with existing experimental data and suggest future experiments. Using these models shows the importance of constraints and state variables in the analysis of behavioral problems.     

Spatial memory and foraging competition in captive western lowland gorillas (Gorilla gorilla gorilla)

Spatial memory and foraging competition were investigated in three mother/offspring pairs of western lowland gorillas,Gorilla gorilla gorilla, using a naturalistic foraging task at the Toronto Zoo. Sixteen permanent food sites were placed throughout the animals’ enclosures. All of the sites were baited and a pair of animals was free to visit the sites and collect the food. Five of the subjects collected the food with accuracy better than chance. Most of the subjects visited the sites using a pattern, and for half the subjects this was one of adjacency. The high accuracy of five of the subjects and the lack of a consistent adjacency pattern suggest that the animals did in fact use spatial memory. Furthermore, the gorillas tended to avoid visiting food sites that had been previously depleted by their partner. They also appeared to split their search of the enclosures, each visiting only a proportion of the food sites. This indicated that the animals were competing and altering their foraging behaviour based on the behaviour of their partner. Therefore, accuracy was recalculated to take this into account. When the sites depleted by either animal in a pair during a given trial were worked into the accuracy calculations for individual animals, three of the animals still maintained accuracy above chance. This suggests that the animals were not only able to remember which sites they had depleted, but those sites depleted by their foraging partner as well.     

Light enough to travel: migratory bats have smaller brains,but not larger hippocampi,than sedentary species

Migratory bird species have smaller brains than non-migratory species. The behavioural flexibility/migratory precursor hypothesis suggests that sedentary birds have larger brains to allow the behavioural flexibility required in a seasonally variable habitat. The energy trade-off hypothesis proposes that brains are heavy, energetically expensive and therefore, incompatible with migration. Here, we compared relative brain, neocortex and hippocampus volume between migratory and sedentary bats at the species-level and using phylogenetically independent contrasts. We found that migratory bats had relatively smaller brains and neocortices than sedentary species. Our results support the energy trade-off hypothesis because bats do not exhibit the same degree of flexibility in diet selection as sedentary birds. Our results also suggest that bat brain size differences are subtler than those found in birds, perhaps owing to bats'' shorter migration distances. Conversely, we found no difference in relative hippocampus volume between migratory and sedentary species, underscoring our limited understanding of the role of the hippocampus in bats.     

Acute and chronic estradiol treatments reduce memory deficits induced by transient global ischemia in female rats

Transient global ischemia induces selective, delayed neuronal death in the hippocampal CA1 and delayed cognitive deficits. Estrogen treatment ameliorates hippocampal injury associated with global ischemia. Although much is known about the impact of estrogen on neuronal survival, relatively little is known about its impact on functional outcome assessed behaviorally. We investigated whether long-term estradiol (21-day pellets implanted 14 days prior to ischemia) or acute estradiol (50 μg infused into the lateral ventricles immediately after ischemia) attenuates ischemia-induced cell loss and improves visual and spatial working memory in ovariectomized female rats. Global ischemia significantly impaired visual and spatial memory, assessed by object recognition and object placement tests at 6-9 days. Global ischemia did not affect locomotion, exploration, or anxiety-related behaviors, assessed by an open-field test at 6 days. Long-term estradiol prevented the ischemia-induced deficit in visual working memory, maintaining normal performance in tests with retention intervals of up to 1 h. Long-term estradiol also prevented ischemia-induced deficits in spatial memory tests with short (1 and 7 min), but not longer (15 min), retention intervals. Acute estradiol significantly improved visual memory assessed with short retention intervals, but did not prevent deficits in spatial memory. Acute estradiol significantly increased the number of surviving CA1 neurons, assessed either at 7 days after ischemia or after the completion of behavioral testing 9 days after ischemia. In contrast, chronic estradiol did not reduce CA1 cell death 9 days after ischemia. Thus, long-term estradiol at near physiological levels and acute estradiol administered after ischemic insult improve functional recovery after global ischemia. These findings have important implications for intervention in the neurological sequellae associated with global ischemia.     

Local and landscape factors determining occurrence of phyllostomid bats in tropical secondary forests

Neotropical forests are being increasingly replaced by a mosaic of patches of different successional stages, agricultural fields and pasture lands. Consequently, the identification of factors shaping the performance of taxa in anthropogenic landscapes is gaining importance, especially for taxa playing critical roles in ecosystem functioning. As phyllostomid bats provide important ecological services through seed dispersal, pollination and control of animal populations, in this study we assessed the relationships between phyllostomid occurrence and the variation in local and landscape level habitat attributes caused by disturbance. We mist-netted phyllostomids in 12 sites representing 4 successional stages of a tropical dry forest (initial, early, intermediate and late). We also quantitatively characterized the habitat attributes at the local (vegetation structure complexity) and the landscape level (forest cover, area and diversity of patches). Two focal scales were considered for landscape characterization: 500 and 1000 m. During 142 sampling nights, we captured 606 individuals representing 15 species and 4 broad guilds. Variation in phyllostomid assemblages, ensembles and populations was associated with variation in local and landscape habitat attributes, and this association was scale-dependent. Specifically, we found a marked guild-specific response, where the abundance of nectarivores tended to be negatively associated with the mean area of dry forest patches, while the abundance of frugivores was positively associated with the percentage of riparian forest. These results are explained by the prevalence of chiropterophilic species in the dry forest and of chiropterochorous species in the riparian forest. Our results indicate that different vegetation classes, as well as a multi-spatial scale approach must be considered for evaluating bat response to variation in landscape attributes. Moreover, for the long-term conservation of phyllostomids in anthropogenic landscapes, we must realize that the management of the habitat at the landscape level is as important as the conservation of particular forest fragments.     

Host-plant selection,diet diversity,and optimal foraging in a tropical leafcutting ant

Summary A month-long study was conducted on the comparative foraging behavior of 20 colonies of the leafcutting ant, Atta cephalotes L. in Santa Rosa National Park, Guanacaste Province, Costa Rica. The study was conducted during the middle of the wet season, when trees had mature foliage and the ants were maximally selective among species of potential host plants. The colonies always gathered leaves from more than a single tree species but on average one species constituted almost half the diet with the remaining species being of geometrically decreasing importance. Colonies exhibited greater diversity in their choice of leaves and lower constancy of foraging when the average quality of resource trees was lower, as predicted by elementary optimal foraging theory. Furthermore, the ants were more selective of the species they attacked at greater distances from the nest. However, the ants sometimes did not attack apparently palatable species, and often did not attack nearby individuals of species they were exploiting at greater distances.A classical explanation for why leafcutting ants exploit distant host trees when apparently equally good trees are nearer, is that the ants are pursuing a strategy of conserving resources to avoid long-term overgrazing pressure on nearby trees. We prefer a simpler hypothesis: (1) Trees of exploited species exhibit individual variation in the acceptability of their leaves to the ants. (2) The abundance of a species will generally increase with area and radial distance from the nest, so the probability that at least one tree of the species will be acceptable to the ants also increases with distance. (3) The ants forage using a system of trunk-trails cleared of leaf litter, which significantly reduces their travel time to previously discovered, high-quality resource trees (by a factor of 4- to 10-fold). (4) Foragers are unware of the total pool of resources available to the colony. Therefore once scouts have chanced upon a tree which is acceptable, the colony will concentrate on harvesting from that tree rather than searching for additional sources of leaves distant from the established trail.     

Foraging time and spatial patterns of predation in experimental populations

Summary Responses of the predaceous mites Phytoseiulus persimilis, Typhlodromus (=Metaseiulus) occidentalis, and Amblyseius andersoni to spatial variation in egg density of the phytophagous mite, Tetranychus urticae, were studied in the laboratory.The oligophagous predator P. persimilis showed initially a direct density dependent foraging time allocation and variation in foraging time increased with prey density. With changes in prey density due to predation, predator foraging rates (per hour) decreased with time and density dependent foraging gradually became density independence, because P. persimilis continued to respond to initial prey density, instead of the changing prey density and distribution. The consequent spatial pattern of predation by P. persimilis was density independent, although slopes of predation rate-prey density regressions increased with time.Compared with P. persimilis, the narrowly polyphagous predator T. occidentalis responded relatively slowly to the the presence or absence of prey eggs but not to prey density: the mean and variation of foraging time spent in patches with prey did not differ with prey density, but was significantly greater in patches with prey eggs than in patches without eggs. Prey density and distribution changed only slightly due to predation and overall foraging rates remained more or less constant. The consequent spatial pattern of predation by T. occidentalis was inversely density dependent. As with P. persimilis, slopes of predation rate-prey density regressions increased with time (i.e. the inverse density dependence in T. occidentalis became weaker through time).The broadly polyphagous predator A. andersoni showed density independent foraging time allocation with variation independent of prey density. With changes in prey density over time due to prey depletion, overall foraging rates decreased. The consequent spatial pattern of predation by A. andersoni also changed through time; it initially was inversely density dependent, but soon became density independent.Overall, P. persimilis and T. occidentalis spent more time in prey patches than A. andersoni, suggesting that A. andersoni tended to spend more time moving outside patches. The overall predation rates and searching efficiency were higher in P. persimilis than in A. andersoni and T. occidentalis. Predator reproduction was highest in P. persimilis, lower in T. occidentalis and the lowest A. andersoni.The differences in response to prey distribution among the three predaceous species probably reflect the evolution of these species in environments with different patterns of prey distribution. The degree of polyphagy is a major determinant of the aggregative response, but other attributes such as handling time are also important in other aspects of phytoseiid foraging behavior (e.g. searching efficiency or predation rate).     

Energetic cost of hovering flight in nectar-feeding bats (Phyllostomidae: Glossophaginae) and its scaling in moths, birds and bats

Three groups of specialist nectar-feeders covering a continuous size range from insects, birds and bats have evolved the ability for hovering flight. Among birds and bats these groups generally comprise small species, suggesting a relationship between hovering ability and size. In this study we established the scaling relationship of hovering power with body mass for nectar-feeding glossophagine bats (Phyllostomidae). Employing both standard and fast-response respirometry, we determined rates of gas exchange in Hylonycteris underwoodi (7 g) and Choeronycteris mexicana (13–18 g) during hover-feeding flights at an artificial flower that served as a respirometric mask to estimate metabolic power input. The O₂ uptake rate (V˙ _o2) in ml g⁻¹ h⁻¹ (and derived power input) was 27.3 (1.12 W or 160 W kg⁻¹) in 7-g Hylonycteris and 27.3 (2.63 W or 160 W kg⁻¹) in 16.5-g Choeronycteris and thus consistent with measurements in 11.9-g Glossophagasoricina (158 W kg⁻¹, Winter 1998). V˙ _o2 at the onset of hovering was also used to estimate power during forward flight, because after a transition from level forward to hovering flight gas exchange rates initially still reflect forward flight rates. V˙ _o2 during short hovering events (<1.5 s) was 19.0 ml g⁻¹ h⁻¹ (1.8 W) in 16-g Choeronycteris, which was not significantly different from a previous, indirect estimate of the cost of level forward flight (2.1 W, Winter and von Helversen 1998). Our estimates suggest that power input during hovering flight P _h (W) increased with body mass M (kg) within 13–18-g Choeronycteris (n = 4) as P _h  = 3544 (±2057 SE) M ^{1.76 (±0.21 SE)} and between different glossophagine bat species (n = 3) as P _h  = 128 (±2.4 SE) M ^{0.95 (±0.034 SE)}. The slopes of three scaling functions for flight power (hovering, level forward flight at intermediate speed and submaximal flight power) indicate that: 1. The relationship between flight power to flight speed may change with body mass in the 6–30-g bats from a J- towards a U-shaped curve. 2. A metabolic constraint (hovering flight power equal maximal flight power) may influence the upper size limit of 30–35 g for this group of flower specialists. Mass-specific power input (W kg⁻¹) during hovering flight appeared constant with regard to body size (for the mass ranges considered), but differed significantly (P < 0.001) between groups. Group means were 393 W kg⁻¹ (sphingid moths), 261 W kg⁻¹ (hummingbirds) and 159 W kg⁻¹ (glossophagine bats). Thus, glossophagine bats expend the least metabolic power per unit of body mass supported during hovering flight. At a metabolic power input of 1.1 W a glossophagine bat can generate the lift forces necessary for balancing 7 g against gravitation, whereas a hummingbird can support 4 g and a sphingid moth only 3 g of body mass with the same amount of metabolic energy. These differences in power input were not fully explained by differences in induced power output estimated from Rankine-Froude momentum-jet theory. Accepted: 10 November 1998