Morphological and behavioral antipredatory adaptations of decapod zoeae

Summary Zoeae of some species of estuarine decapods are retained in the estuary throughout development while others are exported into nearshore coastal waters. The horizontal migrations of decapod zoeae to coastal waters may have evolved to reduce the probability of encountering planktivorous fishes which are most abundant in the estuary. If so, then the morphological vulnerability of zoeae to fish predation should be inversely related to the number of predators occurring where they develop. Six species of estuarine decapod zoeae were offered to Menidia menidia and Fundulus heteroclitus. The behavioral interactions were observed to determine the prey's vulnerability to predation, and the mode of operation and relative effectiveness of their defenses. Feeding trials and behavioral observations both demonstrated that M. menidia 6–16 mm long preferred Uca minax and Callinectes sapidus zoeae, which are exported from the estuary, to Rhithropanopeus harrisii, Sesarma reticulatum and Palaemonetes pugio, which are retained within estuaries. Pinnotheres ostreum zoeae develop in the lower estuary and fish demonstrated an intermediate preference for the zoeae. Menidia menidia 20–40 mm long showed similar preferences for R. harrisii S. reticulatum, P. ostreum and U. minax as did small silversides. Large-mouthed demersal fish, Fundulus heteroclitus 6–10 mm long, also preferred U. minax to R. harrisii, but more readily preyed on zoeae than did M. menidia. The exported species of zoeae have shorter spines and smaller bodies than do retained zoeae, except P. ostreum which is small, spineless and passively sinks when attacked by fish. Other retained species of zoeae also have postcontact behavioral defenses which enhance the effectiveness of their morphological defenses. Zoeae do not evade attacks by fishes, but fishes quickly learned to avoid zoeae, which increases the effectiveness of the zoeae's antipredatory adaptations.     

Atelinae adaptations: behavioral strategies and ecological constraints.

Comparisons between the four genera that make up the Atelinae reveal two distinct behavioral patterns, one in which energy expenditure is minimized (Alouatta) and one in which energy intake is maximized (Lagothrix, Ateles, and Brachyteles). Among the atelins, Lagothrix and Ateles devote over 75% of their annual feeding time to fruit, while Brachyteles devotes between 50% and 67% of their feeding time to leaves. Pronounced seasonality in the Atlantic coastal forest inhabited by Brachyteles may be responsible for its more folivorous diet. Alouatta falls in the body size range of Lagothrix and is much smaller than Ateles and Brachyteles. Nonetheless, Alouatta is more folivorous than sympatric atelins. The atelins also share a rapid, suspensory mode of locomotion that appears to enable them to minimize travel time between widely dispersed fruit sources. Alouatta, by contrast, employs a slower, but more energetically efficient, quadrupedal locomotion. Ranging patterns among the Atelinae are consistent with both diet and locomotor abilities: Atelins travel daily distances up to 5,000 m; Alouatta ranges are much shorter. Further distinctions are evident in Atelinae grouping patterns. Alouatta remains in small cohesive groups that occupy home ranges less than 60 ha in size. Both Lagothrix and Ateles have large groups that fission to reduce the costs of intragroup feeding competition when preferred fruits occur in small patches within much larger community ranges. While greater reliance on low-energy foods such as leaves may release Brachyteles from similar competitive constraints, their tendency toward fluid grouping associations is consistent with the pursuit of a frugivorous diet.     

Climatic adaptations of body melanisation in Drosophila melanogaster from Western Himalayas

We investigated population divergence in body melanisation in wild samples of Drosophila melanogaster across an elevational gradient (512-2202 m) in the Western Himalayas. Wild populations are characterized by higher phenotypic variability as compared with laboratory populations. Significant differences in elevational slope values for three posterior abdominal segments (fifth, sixth and seventh) in wild versus laboratory populations suggest plastic effects. However, elevational slope values do not differ for the three anterior abdominal segments (second, third and fourth). Thus, elevational changes in melanisation include genetic as well as plastic effects. Fitness consequences of within population variability were analyzed on the basis of assorted darker and lighter flies from two highlands as well as from two lowland localities. There is lack of correlation of melanisation with body size as well as ovariole number in assorted darker and lighter flies. For each population, darker flies showed higher desiccation resistance, lower rate of water loss, longer copulation duration and greater fecundity as compared with lighter flies. Phenotypic variations in body melanisation can be interpreted in relation with seasonal changes in temperature as well as humidity (Tcv and RHcv) of the sites of origin of populations. Thus, elevational changes in body melanisation may represent genetic response to selection pressures imposed by colder and drier climatic conditions in the Western Himalayas.     

Role for GDNF in biochemical and behavioral adaptations to drugs of abuse

The present study examined a role for GDNF in adaptations to drugs of abuse. Infusion of GDNF into the ventral tegmental area (VTA), a dopaminergic brain region important for addiction, blocks certain biochemical adaptations to chronic cocaine or morphine as well as the rewarding effects of cocaine. Conversely, responses to cocaine are enhanced in rats by intra-VTA infusion of an anti-GDNF antibody and in mice heterozygous for a null mutation in the GDNF gene. Chronic morphine or cocaine exposure decreases levels of phosphoRet, the protein kinase that mediates GDNF signaling, in the VTA. Together, these results suggest a feedback loop, whereby drugs of abuse decrease signaling through endogenous GDNF pathways in the VTA, which then increases the behavioral sensitivity to subsequent drug exposure.     

Climatic adaptations of body melanisation in Drosophila melanogaster from Western Himalayas

We investigated population divergence in body melanisation in wild samples of Drosophila melanogaster across an elevational gradient (512 - 2202m) in the Western Himalayas. Wild populations are characterized by higher phenotypic variability as compared with laboratory populations. Significant differences in elevational slope values for three posterior abdominal segments (5th, 6th and 7th) in wild versus laboratory populations suggest plastic effects. However, elevational slope values do not differ for the three anterior abdominal segments (2nd, 3rd and 4th). Thus, elevational changes in melanisation include genetic as well as plastic effects. Fitness consequences of within population variability were analyzed on the basis of assorted darker and lighter flies from two highland as well as from two lowland localities. There is lack of correlation of melanisation with body size as well as ovariole number in assorted darker and lighter flies. For each population, darker flies showed higher desiccation resistance, lower rate of water loss, longer copulation duration and greater fecundity as compared with lighter flies. Phenotypic variations in body melanisation can be interpreted in relation with seasonal changes in temperature as well as humidity (Tcv and RHcv) of the sites of origin of populations. Thus, elevational changes in body melanisation may represent genetic response to selection pressures imposed by colder and drier climatic conditions in the Western Himalayas.     

Two thermosensors in Drosophila have different behavioral functions

Insects inhabit extreme temperature environments and have evolved mechanisms to survive there. Small insects are especially susceptible to rapid changes in body temperature. Therefore, the rapid detection of environment and body temperature is important for their survival. Little, however, is known about the thermosensors that detect those temperatures. Using rapid thermosensitivity assays with temperature step gradients and a spatial learning paradigm (the heat-box) in which elevated temperature serves as the negative reinforcer, two thermosensors were identified and their behavioral functions assessed. A low-temperature thermosensor is located on the antenna, detects relatively low temperatures, and can detect spatial temperature gradients directly. Thus, the antennae can be used by Drosophila to quickly orient with respect to temperature cues. A high-temperature thermosensor of unknown location appears to have a roughly similar sensitivity to temperature differences as the low-temperature thermosensor (< or = 3 degrees C) and is both necessary and sufficient for memory formation in the heat-box spatial learning paradigm. Therefore, the high-temperature thermosensor is important for remembering spatial positions in which dangerously high temperatures were encountered.     

Pheromonal and behavioral cues trigger male-to-female aggression in Drosophila

Appropriate displays of aggression rely on the ability to recognize potential competitors. As in most species, Drosophila males fight with other males and do not attack females. In insects, sex recognition is strongly dependent on chemosensory communication, mediated by cuticular hydrocarbons acting as pheromones. While the roles of chemical and other sensory cues in stimulating male to female courtship have been well characterized in Drosophila, the signals that elicit aggression remain unclear. Here we show that when female pheromones or behavior are masculinized, males recognize females as competitors and switch from courtship to aggression. To masculinize female pheromones, a transgene carrying dsRNA for the sex determination factor transformer (traIR) was targeted to the pheromone producing cells, the oenocytes. Shortly after copulation males attacked these females, indicating that pheromonal cues can override other sensory cues. Surprisingly, masculinization of female behavior by targeting traIR to the nervous system in an otherwise normal female also was sufficient to trigger male aggression. Simultaneous masculinization of both pheromones and behavior induced a complete switch in the normal male response to a female. Control males now fought rather than copulated with these females. In a reciprocal experiment, feminization of the oenocytes and nervous system in males by expression of transformer (traF) elicited high levels of courtship and little or no aggression from control males. Finally, when confronted with flies devoid of pheromones, control males attacked male but not female opponents, suggesting that aggression is not a default behavior in the absence of pheromonal cues. Thus, our results show that masculinization of either pheromones or behavior in females is sufficient to trigger male-to-female aggression. Moreover, by manipulating both the pheromonal profile and the fighting patterns displayed by the opponent, male behavioral responses towards males and females can be completely reversed. Therefore, both pheromonal and behavioral cues are used by Drosophila males in recognizing a conspecific as a competitor.     

Awakening to the behavioral analysis of sleep in Drosophila

Perhaps the most observable of the many circadian oscillations that have been described in both vertebrate and invertebrate animals is the daily alterations in periods of rest and activity. Recent studies in the fruit fly Drosophila melanogaster suggest that these periods of inactivity are not simply rest but share many of the fundamental components that define mammalian sleep. Thus, quiescent episodes are characterized by reduced awareness of the environment and are homeostatically regulated. Although this field is in its infancy, recent studies have focused on the interaction between circadian and homeostatic processes. These results indicate that components of the circadian clock may play a substantial role in mechanisms underlying sleep homeostasis at the molecular level. In this article, the author reviews recent advances obtained using Drosophila as a model system to elucidate fundamental components of sleep regulation.     

The nonA gene in Drosophila conveys species-specific behavioral characteristics

The molecular basis of species-specific differences in courtship behavior, a critical factor in preserving species boundaries, is poorly understood. Genetic analysis of all but the most closely related species is usually impossible, given the inviability of hybrids. We have therefore applied interspecific transformation of a single candidate behavioral locus, no-on-transient A (nonA), between Drosophila virilis and D. melanogaster, to investigate whether nonA, like the period gene, might encode species-specific behavioral information. Mutations in nonA can disrupt both visual behavior and the courtship song in D. melanogaster. The lovesong of nonA(diss) mutant males superficially resembles that of D. virilis, a species that diverged from D. melanogaster 40-60 mya. Transformation of the cloned D. virilis nonA gene into D. melanogaster hosts carrying a synthetic deletion of the nonA locus restored normal visual function (the phenotype most sensitive to nonA mutation). However, the courtship song of transformant males showed several features characteristic of the corresponding D. virilis signal, indicating that nonA can act as a reservoir for species-specific information. This candidate gene approach, together with interspecific transformation, can therefore provide a direct avenue to explore potential speciation genes in genetically and molecularly tractable organisms such as Drosophila.     

Phylogenetic relationships and climatic adaptations in the Drosophila takahashii and montium species subgroups

We analyze phylogenetic relationships among temperate, subtropical highland, and subtropical lowland species of the Drosophila takahashii and montium species subgroups based on sequence data of COI and Gpdh genes and discuss the evolution of temperate species in these subgroups with reference to their climatic adaptations. In the takahashii subgroup, D. lutescens (the temperate species) branched off first in the tree based on the combined data set, but D. prostipennis (the subtropical highland species) branched off first in the trees based on single genes. Thus, phylogenetic relationships in this subgroup are still ambiguous. In the montium subgroup, the cool-temperate species are phylogenetically close to the warm-temperate species, and these cool- and warm-temperate species form a cluster with the subtropical highland species. This suggests that perhaps the cool-temperate species derived from the warm-temperate species and the warm-temperate species derived from the subtropical highland species. In comparison with the subtropical lowland species, the subtropical highland species may be better able to colonize temperate areas since, as in the temperate species, they have an ability to develop their ovaries at moderately low temperature. However, the subtropical highland species, as well as the subtropical lowland species, were much less cold tolerant than the temperate species. Therefore, considerable genetic reformation would be required for both the subtropical highland and the subtropical lowland species to adapt to temperate climates.     

Surviving winter hypoxia: behavioral adaptations of fishes in a northern Wisconsin winterkill lake

Synopsis Winterkill lakes often have a characteristic fish community, presumably composed of species able to survive winter hypoxia. Our research on a small winterkill lake in northern Wisconsin indicates that fishes common in winterkill lakes have behavioral adaptations for tolerating or avoiding winter hypoxia. We examined the distribution of fishes within the lake during one winter (December through May), and fish migrations into and out of the lake for two consecutive years. As DO within the lake declined in late fall, adult-sized fishes of four species, brook stickleback, finescale dace, redbelly dace, and fathead minnow, moved to the ice-water interface where DO levels were highest. Stickleback, and to a lesser extent, fathead minnows, also moved toward the more highly oxygenated water near the inlet. During the first year, young-of-the-year fishes of blacknose shiner, Iowa darter, redbelly dace, and fathead minnow, avoided hypoxic conditions by emigrating from the lake via the outlet stream in late fall and early winter while DO within the lake was still relatively high. Blacknose shiner, redbelly dace, and fathead minnow returned to the lake in spring. Almost no fishes were trapped leaving the lake in the second fall-winter season. Central mudminnows neither moved to the ice-water interface nor emigrated from the lake as DO dropped. Mudminnows survive winter hypoxia by breathing oxygen-containing bubbles trapped beneath the ice. These relatively simple behavioral adaptations allow fishes to survive or avoid hypoxic conditions lethal to other species and may help explain the consistency in fish communities of winterkill lakes.     

Winter space use of coyotes in high-elevation environments: behavioral adaptations to deep-snow landscapes

In the last century, coyotes (Canis latrans) have expanded their range geographically, but have also expanded their use of habitats within currently occupied regions. Because coyotes are not morphologically adapted for travel in deep snow, we studied coyote space use patterns in a deep-snow landscape to examine behavioral adaptations enabling them to use high elevations during winter. We examined the influence of snow depth, snow penetrability, canopy cover, and habitat type, as well as the rates of prey and predator track encounters, on coyote travel distance in high-elevation terrain in northwestern Wyoming, USA. We backtracked 13 radio-collared coyotes for 265.41 km during the winters of 2006–2007 and 2007–2008, and compared habitat use and movement patterns of the actual coyotes with 259.11 km of random travel paths. Coyotes used specific habitats differently than were available on the landscape. Open woodlands were used for the majority of coyote travel distance, followed by mixed conifer, and closed-stand spruce–fir. Prey track encounters peaked in closed-stand, mature Douglas fir, followed by 50- to 150-year-old lodgepole pine stands, and 0- to 40-year-old regeneration lodgepole pine stands. Snowmobile trails had the most variation between use and availability on the landscape (12.0 % use vs. 0.6 % available). Coyotes increased use of habitats with dense canopy cover as snow penetration increased and rates of rodent and red squirrel track encounters increased. Additionally, coyotes spent more time in habitats containing more tracks of ungulates. Conversely, use of habitats with less canopy cover decreased as snow depth increased, and coyotes traveled more directly in habitats with less canopy cover and lower snow penetration, suggesting coyotes used these habitats to travel. Coyotes persisted throughout the winter and effectively used resources despite deep snow conditions in a high-elevation environment.     

Temporal mating isolation driven by a behavioral gene in Drosophila

Speciation is the evolutionary process in which new barriers to gene exchange are created. These barriers may be physical, leading to spatial separation of subpopulations and resulting in allopatric speciation, or they may be temporal, giving rise to allochronic speciation, and may include the time of day or the time of year when mating takes place. Drosophila melanogaster and D. pseudoobscura show different temporal patterns of circadian locomotor activity that are determined by the circadian clock gene period (per). Genes that control aspects of behavior that might be relevant to courtship and mating, such as locomotor patterns, become obvious candidates for involvement in the speciation process. However, evidence for the role of individual genes in the mechanism of mate choice has proved elusive. We have used transgenic flies carrying the natural per genes from these two Drosophila species to reveal that per has the potential to provide the permissive conditions for speciation, by affecting mate choice through a mechanism involving the species-specific timing of mating behavior.     

Complex brain and behavioral functions disrupted by mutations in Drosophila

Reproductive behavior in Drosophila involves a complex series of actions which is perturbed by many different kinds of mutations. Some of the most interesting courtship variants are those originally isolated with respect to disruptions of general learning and memory. Several types of genetically abnormal males have their “conditioned courtship” blocked or attenuated by the learning and memory mutations, some of which, in turn, are known to cause abnormal levels of specific monoamines or cyclic nucleotides. Recent studies of the defective courtship performed by the conditioning mutants involve “mosaic focusing” of the neural tissues affected by the behavioral/biochemical mutations. These experiments address the question of whether there are localized influences of the relevant genetic loci in their control of conditioned courtship, in spite of the fact that the protein products of the genes have a broad tissue distribution. Female responses to courting Drosophila males can also be dependent on the former's prior experiences. This pertains to enhancing aftereffects of prestimulation by the courtship song that is produced by a male; and the same learning and memory mutations, expressed in females, impinge on the normal aftereffects. One element of acoustical communication in courtship is a rhythmic oscillation in a particular component of the song. This short-term behavioral rhythm is altered in males expressing circadian rhythm mutations. To investigate the neural and cellular mechanisms by which these genes act, a mosaic analysis has been initiated on the ganglia affected by a clock mutation in its disruption of the courtship rhythm and of circadian cycles. A molecular isolation and identification of the normal form of this genecalled period—has also begun, in order to probe the locus's structure and function in detail. Such an investigation will include a comparison of the mosaic results with a direct determination of the various tissues in which the gene's product is expressed. In addition, interspecific transfers of the purified period gene will augment the current studies of species-specific features of the rhythmic courtship songs.     

A behavioral odor similarity "space" in larval Drosophila

To provide a behavior-based estimate of odor similarity in larval Drosophila, we use 4 recognition-type experiments: 1) We train larvae to associate an odor with food and then test whether they would regard another odor as the same as the trained one. 2) We train larvae to associate an odor with food and test whether they prefer the trained odor against a novel nontrained one. 3) We train larvae differentially to associate one odor with food, but not the other one, and test whether they prefer the rewarded against the nonrewarded odor. 4) In an experiment like (3), we test the larvae after a 30-min break. This yields a combined task-independent estimate of perceived difference between odor pairs. Comparing these perceived differences to published measures of physicochemical difference reveals a weak correlation. A notable exception are 3-octanol and benzaldehyde, which are distinct in published accounts of chemical similarity and in terms of their published sensory representation but nevertheless are consistently regarded as the most similar of the 10 odor pairs employed. It thus appears as if at least some aspects of olfactory perception are "computed" in postreceptor circuits on the basis of sensory signals rather than being immediately given by them.     

Life history adaptations and stress tolerance of four domestic species of Drosophila

Life history traits and stress tolerance were studied in four domestic species of Drosophila–D. melanogaster, D. simulans, D. auraria and D. immigrans– to understand how they adapt to their environments. In all species, larval weight approximately doubled in 1 day. The relative egg weight (egg weight : pupal weight) was smaller and the larval period was longer in D. immigrans than in the other three species. The pupal period was the longest in D. auraria. However, the adaptive significance of these differences in larval and pupal periods was not clear. The pupal case was generally thicker in the larger species, probably to support the larger pupal body. The start of oviposition was earliest and reproductive effort was greatest in female D. simulans, followed by female D. melanogaster. In contrast, starvation tolerance and the increase in bodyweight after eclosion was greater in D. immigrans and D. auraria than in the other two species. Pupal desiccation tolerance was greatest in D. melanogaster and lowest in D. auraria, and the less tolerant species seemed to select more humid sites for pupation. Adult tolerance to desiccation was greatest in D. melanogaster and lowest in D. simulans. In contrast, adult cold tolerance was greater in D. auraria and adult heat tolerance was lower in D. immigrans than in the other species. These differences in life history traits and stress tolerance represent the Drosophila species differential adaptations, and are assumed to allow coexistence of the species.