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The genetics and epigenetic processes associated with morphological organization are a principal aim of biology, ranging from cohesion between cells to shape and size of organisms. We investigate the post-embryonic development of Hypopharyngeal sclerite and cornua HPC and mandibles M of Drosophila gaucha larva. Integrated functioning of these Cephalopharyngeal skeleton parts of D. gaucha larva is essential for food acquisition, participating in locomotion and microhabitat selection. We examined two isolates by recording the growth of the HPC and M every 24 h for 8 days in parental, F1, F2 and backcross larvae. In F1 larvae, the HPC and M growth was similar to the parental. In F2 and backcross larvae, the growth was slower. Epistasis and dominance are the principal sources upon which the growth of HPC and M are based. Pleiotropic genes seem also to be involved in integrating the development of M and HPC. Our data suggest that hybridization of the isolates modified epigenetic processes involved in the development of those morphological structures of D. gaucha larva.

We investigated pupa distributions of D. simulans, D. buzzatii, D. melanogaster, D. immigrans and D. hydei on a number of natural breeding sites. Pupae of all five species showed aggregated distributions, which prompted us to examine these aggregations in a more detail for two species that commonly co-occur in breeding sites, D. simulans and D. buzzatii. We found that pupae of both species tend to be aggregated in conspecific clusters. Subsequent experiments revealed that both species are attracted to the odors of other larvae, though only D. buzzatii differentiated between conspecifics and heterospecifics (they preferred conspecific). Furthermore, third instar larvae of both species preferred more alkaline substrates. Altogether, our results demonstrate that Drosophila species form conspecific pupa aggregations in natural breeding sites, and that pupation site selection depends on interactions among conspecific and heterospecific larvae and on chemical characteristics of the breeding sites.

We investigated the role of Drosophila larva olfactory system in identification of congeners and aliens. We discuss the importance of these activities in larva navigation across substrates, and the implications for allocation of space and food among species of similar ecologies. Wild type larvae of cosmopolitan D. melanogaster and endemic D. pavani, which cohabit the same breeding sites, used species-specific volatiles to identify conspecifics and aliens moving toward larvae of their species. D. gaucha larvae, a sibling species of D. pavani that is ecologically isolated from D. melanogaster, did not respond to melanogaster odor cues. Similar to D. pavani larvae, the navigation of pavani female x gaucha male hybrids was influenced by conspecific and alien odors, whereas gaucha female x pavani male hybrid larvae exhibited behavior similar to the D. gaucha parent. The two sibling species exhibited substantial evolutionary divergence in processing the odor inputs necessary to identify conspecifics. Orco (Or83b) mutant larvae of D. melanogaster, which exhibit a loss of sense of smell, did not distinguish conspecific from alien larvae, instead moving across the substrate. Syn 97CS and rut larvae of D. melanogaster, which are unable to learn but can smell, moved across the substrate as well. The Orco (Or83b), Syn 97CS and rut loci are necessary to orient navigation by D. melanogaster larvae. Individuals of the Trana strain of D. melanogaster did not respond to conspecific and alien larval volatiles and therefore navigated randomly across the substrate. By contrast, larvae of the Til-Til strain used larval volatiles to orient their movement. Natural populations of D. melanogaster may exhibit differences in identification of conspecific and alien larvae. Larval locomotion was not affected by the volatiles.

We investigated dispersal patterns of Drosophila larvae searching for pupation sites over three substrates to determine the role of spatial heterogeneity and presence of other species on prepupation behavior. We used D. melanogaster, D. hydei, and D. pavani whose parents emerged from apples collected in one orchard. Each species showed different preferences for substrates on which to pupate, particularly in the presence of another Drosophila species. Larval locomotion rate and turning behavior in D. melanogaster, D. hydei, and D. pavani were modified depending this upon the type of substrate (agar and sand) on which the larvae crawled. These two behaviors are involved in dispersal and aggregation of pupae. Distance between pupae of the same species decreases when larvae of another species pupate on the same substrate. Aggregated distributions over the substrates lead to patches with few or no individuals. These could serve as pupation sites for other Drosophila species that, in nature, also emerge from small breeding sites. Key words: breeding sites, pupation behavior, sympatric Drosophila species. [Behav Ecol]

Many species of Drosophila form conspecific pupa aggregations across the breeding sites. These aggregations could result from species-specific larval odor recognition. To test this hypothesis we used larval odors of D. melanogaster and D. pavani, two species that coexist in the nature. When stimulated by those odors, wild type and vestigial (vg) third-instar larvae of D. melanogaster pupated on conspecific larval odors, but individuals deficient in the expression of the odor co-receptor Orco randomly pupated across the substrate, indicating that in this species, olfaction plays a role in pupation site selection. Larvae are unable to learn but can smell, the Syn97CS and rut strains of D. melanogaster, did not respond to conspecific odors or D. pavani larval cues, and they randomly pupated across the substrate, suggesting that larval odor-based learning could influence the pupation site selection. Thus, Orco, Syn97CS and rut loci participated in the pupation site selection. When stimulated by conspecific and D. melanogaster larval cues, D. pavani larvae also pupated on conspecific odors. The larvae of D. gaucha, a sibling species of D. pavani, did not respond to D. melanogaster larval cues, pupating randomly across the substrate. In nature, D. gaucha is isolated from D. melanogaster. Interspecific hybrids, which result from crossing pavani female with gaucha males clumped their pupae similarly to D. pavani, but the behavior of gaucha female x pavani male hybrids was similar to D. gaucha parent. The two sibling species show substantial evolutionary divergence in organization and functioning of larval nervous system. D. melanogaster and D. pavani larvae extracted information about odor identities and the spatial location of congener and alien larvae to select pupation sites. We hypothesize that larval recognition contributes to the cohabitation of species with similar ecologies, thus aiding the organization and persistence of Drosophila species guilds in the wild.

The development of larval foraging behaviour in the sibling species D. pavani and D. gaucha and in their reciprocal interspecific hybrids was analysed. The goals were: (i) to identify interspecific differences in developmental patterns of larval behavioural organization, and (ii) to study changes in the frequency of ecologically relevant behaviours during larval ontogeny. Hybridization changed the developmental pathway of feeding and locomotor activity, suggesting genetic divergence for foraging behaviour between the species. Larval turning and bending were not affected by hybridization, suggesting a similar genetic architecture for each of these activities in both species. Retreat and rearing were observed during the whole of larval period in D. pavani, while these behaviours were rarely observed in D. gaucha and the hybrids, suggesting dominance of the gaucha genome over that of pavani. The behavioural organization of D. pavani larvae is related to ontogeny; this was not observed in gaucha and in species hybrid larvae, suggesting again a dominance of this genome over that of D. pavani. The results are discussed in terms of evolutionary developmental genetics of foraging behaviour of Drosophila larvae.

The development of behaviours in larvae of six species of the mesophragmatica group of Drosophila was investigated. The goals were: (i) to uncover patterns of development and evolution of behaviours, and (ii) to establish behavioural phenograms in order to compare them with the phylogenetic relationships based on chromosomal and isoenzymatic marker studies. In the presence of food, feeding, locomotion, turning, rearing, retreat and bending were recorded. During the whole larval period (24-28 to 192-196 h of age) D. mesophragmatica and D. viracochi show clear, regular but contrasting patterns of development for these behaviours. Fluctuations across larval age were observed for the behaviours exhibited by D. pavani, D. gaucha, D. gasici and D. brncici. As larval development progressed the behaviour of the six species became more differentiated. Larvae of the six species also differed in behavioural organization. The preadults of the species showed high recurrence of feeding and locomotion. In D. mesophragmatica, D. viracochi and D. gasici some elements of behaviour tended to occur in triplets of regular sequence, whereas sequences of two elements were observed in larvae of D. pavani and D. brncici. D. gaucha larvae do not show sequential dependency of behavioural elements. Behavioural similarity among the six species tends to follow the phylogenetic relationships established by chromosomal and isoenzymatic studies. The findings suggest that genetic differences among the six species are expressed in the development of larval behaviours.

Abstract The behavioural mechanisms by which the larvae of the sibling species D. pavani and D. gaucha, and their reciprocal hybrids select pupation sites are described in terms of larval substrate preferences. If the larval behaviour of the parental species and their reciprocal hybrids during pupation leads them to pupate in different substrates, such preferences could be used to identify environmental factors and genetic mechanisms involved in the evolution of that behaviour. Confronted with dry substrates, interspecific hybrid larvae pupated in the rearing cup, while the parental species pupated both outside and inside the cup. Like the parental species, the hybrids pupated outside, when humid substrates surrounded the rearing cup. Larvae from D. pavani and D. gaucha showed a broader norm of reaction than the hybrids. D. pavani larvae occupied dry and humid substrates to pupate, while D. gaucha larvae tended to prefer only humid substrates. Larvae of D. pavani burrowed into dry sand pupated preferently in the deep layers of the substrate. Few D. gaucha larvae burrowed; they tended to pupate in the upper layers of dry sand. D. pavani larvae pupated on the moist sand, while most of D. gaucha larvae burrowed and formed puparia in the upper layers of the substrate. The hybrid larvae showed no burrowing behaviour in either dry or moist sand.

International audience; In the wild, larvae of several species of Drosophila develop in heterogeneous and rapidly changing environments sharing resources as food and space. In this scenario, sensory systems contribute to detect, localize and recognize congeners and heterospecifics, and provide information about the availability of food and chemical features of environments where animals live. We investigated the behavior of D. simulans and D. buzzatii larvae to chemicals emitted by conspecific and heterospecific larvae. Our goal was to understand the role of these substances in the selection of pupation sites in the two species that cohabit within decaying prickly pear fruits (Opuntia ficus-indica). In these breeding sites, larvae of D. simulans and D. buzzatii detect larvae of the other species changing their pupation site preferences. Larvae of the two species pupated in the part of the fruit containing no or few heterospecifics, and spent a longer time in/on spots marked by conspecifics rather than heterospecifics. In contrast, larvae of the two species reared in isolation from conspecifics pupated randomly over the substrate and spent a similar amount of time on spots marked by conspecifics and by heterospecifics. Our results indicate that early chemically-based experience with conspecific larvae is critical for the selection of the pupation sites in D. simulans and D. buzzatii, and that pupation site preferences of Drosophila larvae depend on species-specific chemical cues. These preferences can be modulate by the presence of larvae of the same or another species.

Locomotion is a primary means by which animals interact with the world. To understand the contribution of genotype × environment interactions to individual differences in D. melanogaster larval locomotion we investigated phenotypic sensitivity to environmental changes in four strains of this species and their F1 hybrids. We also investigated to what extent flexibility and plasticity of locomotion depend upon larval age. Specifically, we examined larval locomotion at 48 and 96 h of development on three different substrates. Locomotion was influenced by the structure of the substrate, but this depended on both the genotype and larval age. At 48 h of larval development phenotypic variation in locomotion was attributable to both genotype × environment interactions and genotypic differences among the larvae, while at 96 h of age, differences were mainly due to genotype × environment interactions. An analysis of variance of the 4 × 4 diallel cross made at 48 and 96 h of development showed, depending on the cross, either dominance to increase/decrease locomotion, overdominance to increase/decrease locomotion, or no dominance to increase/decrease locomotion. Furthermore, the diversity of behavioral responses in the F1 hybrids was greater at 96 than at 48 h of larval development. Our results demonstrate that genotype × environment interactions result in plasticity of D. melanogaster larval locomotion, which makes sense in light of the fact that larvae, in the wild, develop in heterogeneous and rapidly changing environments.

Abstract. Young Drosophila larvae (24-28 and 48-52 h old) show a preference for feeding in dark environments, while older larvae (72-76 h post-hatching) prefer more illuminated environments. Changes in the photoresponse during larval development are characteristic of D. melanogaster, D. immigrans, D. hydei and D. virilis. In contrast, larvae of D. simulans, D. gaucha, D. pavani and D. funebris show no change in their response to light during larval development, both dispersing and feeding in dark environments. A biometrical analysis of the development of larval photoresponse of D. melanogaster shows that the genetic structure involved in the expression of this behaviour depends on larval age. At 24-28 h of age, additive, dominant and epistatic components were found. At 48-52 h, dominant and epistatic interactions were significant. At 72-76 and 96-100 h of age only non-allelic interactions were important. Thus, epistasis tends to increase as larval development progresses. The concepts of genetic co-adaptation, developmental homeostasis and heritability are discussed in relation to the development of larval photoresponse in D. melanogaster.

Larval foraging behaviour in two sibling species, Drosophila pavani and Drosophila gaucha belonging to the mesophragmatica species group, is described. Interspecific hybrid larvae derived from both reciprocal crosses of the parent species show disruption in the organization of their behaviour, leading to lower mean feeding rates. This, together with interactions involving biotic residues, described elsewhere, is likely under competitive conditions to contribute to reduced fitness of the hybrids relative to the parent species.

To understand the genetics and evolution of foraging in larvae of Drosophila funebris, we examined two strains reared at different breeding sites in the wild. Larvae of the Til-Til strain breed in necrotic cactus tissue, while those of the Pelequen strain rear in necrotic prickly pear cladodes. We measured feeding, locomotion, turning behavior, and latency of D. funebris. Til-Til and Pelequen larvae, at 8 days of age show very similar rates in all behaviors. Crosses between Til-Til and Pelequen strains decrease feeding rate and increase locomotion, turning, and latency in F(1) and F(2) larvae. Backcross larvae show a behavior similar to that of their parental strains. The behavioral similarities observed between the Til-Til and Pelequen strains are product of two different co-adapted gene pools. Epistasis and dominance are the principal sources upon which adaptation of the gene pools of each population are based.

To explore the evolution of higher order behavioral traits we investigated the organization of foraging patterns in first instar larvae of natural populations of Drosophila. We examined Drosophila simulans (cosmopolitan); D. mauritania (widespread); D. pavani, and D. gaucha (endemic). Larvae of these four species share the same behavior components that comprise foraging (locomotion, feeding, bending, and turning). D. simulans and D. mauritania larvae show uncoupled foraging patterns organized into partially independent behavioral elements. Larvae of D. pavani and D. gaucha exhibit coupled foraging behaviors based on a dependency between behavioral components. Hybrid larvae obtained from crosses of natural populations of D. simulans and D. mauritania show an organization of foraging patterns similar to that of the parental lines. In contrast, hybridization disrupts the organization of foraging patterns in D. pavani and D. gaucha intra- and inter-specific hybrid larvae. This suggests genetic co-adaptation for linkage between the behavioral components that comprise foraging. The organization of larval foraging patterns of the endemic species D. pavani seems readily affected by hybridization. The absence of linkage between behavioral components, as in the case of larval foraging patterns of D. simulans and D. mauritania could lead to an increase in the variability of organization of this higher order behavior. The possibility that larvae may use a variable and flexible behavioral integration of foraging patterns could contribute to their development and feeding in a diversity of substrates and climates.

Flies from two populations of the Chilean endemic neotropical species Drosophila pavani and two populations of its sibling species Drosophila gaucha were crossed reciprocally to obtain intra- and interspecific hybrids. The developmental pathways of locomotor activity and feeding rate were analysed for eleven of twelve possible genotype groups. The hybrids showed reduced fitness indicated by a decrease in the measured traits. Hybrid disadvantage was strongest in interspecific hybrids, especially with respect to feeding behaviour. This evidence supports the contention that D. pavani and D. gaucha have evolved different coadapted gene pools controlling the developmental pathways for behavioural traits expressed during larval foraging; but genetic divergence affecting these behaviours has also taken place between locally adapted populations within each species.

Larvae of the sibling species Drosophila simulans and D. mauritiana have rates of locomotor and feeding activity that are closely similar. Comparisons of the trait means for intra- and interspecific hybrids show that significant epistatic interactions affect both characters when the genomes of the two species are combined. The phenotypic variances of progenies obtained by backcrossing the interspecific hybrids to their respective parent species show that appreciable genetic turnover affecting foraging behaviour has occurred since their two phylogenetic lines diverged.

The yellow (y) mutation of Drosophila melanogaster affects the development of behavior and morphology. We have analyzed some behavioral and morphological parameters during the development of y mutants. Wild-type third instar larvae move in straighter paths than larvae of the same age homozygous for the y mutation. At 96 h of age, the tracks of y larvae have 10 times as many loops as tracks of wild-type larvae, and at 120 h of age, y larvae show bending behavior about 2.5 times more frequently than do wild-type. Consequently, they do not disperse as much as wild-type larvae. Concomitant with the behavioral changes, the larvae present a defect in the morphology of large chaetae in the larval denticle belts, particularly of 2nd and 3rd instars, both with light and scanning electron microscopes. These results suggest that a cuticular defect is probably involved in the abnormal locomotor activity observed in y larvae of Drosophila melanogaster.

Digging behavior of D. melanogaster larvae increases as larval development proceeds. Diallel crosses were made to analyze genetically digging behavior at 72 and 108 h of larval age. Additive and dominance variation was found, dominance being principally to dig. Dominance to dig is higher at 108 than 72 h of development; additivity does not substantially change between these two larval ages. At 72 h of larval age, depending on the cross, I found (i) dominance to dig, (ii) dominance to nondig, (iii) overdominance to dig, and (iv) no dominance to dig. At 108 h of larval development I detected (i) dominance to dig and (ii) overdominance to dig. Thus, diversity of response in the F1 was greater at 72 than 108 h of larval development. These age-related changes in larval digging behavior of D. melanogaster seem to reflect epigenetic changes in the patterns of gene expressions.

The digging behavior of larvae from the following strains of Drosophila melanogaster was studied: Oregon R-c, taxi, yellow, and vestigial. It was found that the time of stay of preadults in the culture medium, the number of larvae, and the illumination conditions can modify this behavior. The presence of this characteristic depends on the genetic composition of the population: the larvae of each strain used exhibited their own particular pattern of dispersal throughout the culture medium, independent of the experimental conditions under which this behavior was surveyed.

A survey in the development of larval movement patterns of D. melanogaster and D. simulans wild stocks was made. Larval movement patterns of four lines of D. melanogaster genetically selected for fast and slow feeding rate were also examined. The following behavioural elements were considered: locomotion, turning behaviour and number of larvae moving within a small area (“sitter” larvae). Because locomotion increases with larval age whilst turning does not substantially change between 24 to 96 hours of age, the larval movement pattern of Drosophila tends to be straighter as development proceeds. In the absence of food, Drosophila larvae increase locomotion and decrease turning. The opposite situation occurs when larvae are deposited on a nutritive substrate. However, larvae of a slow feeding line (SA) have a modified pattern of movement in the presence and in the absence of food. Orthokinesis and klinokinesis were more obvious in D. simulans larvae. Quantitative differences in the larval movement pattern of these two sibling species were greater on a nutritive medium. In both species the percentage of “sitter” larvae increases in the presence of food, particularly in D. simulans. This increase depends on larval age. Crosses between two D. melanogaster strains, which differ in larval turning, suggest that one pair of major additive genetic factors control this behaviour. The adaptative nature of larval movement patterns of Drosophila is discussed.

The genetics of the digging behavior of Drosophila melanogaster larvae was studied through selective breeding. Selection for low digging activity was successful, but selection for high digging activity was not. Selection for low and high digging activity affected another behavior, namely the choice of a pupation site. Digging behavior appears to be under polygenic control.

Larval prepupation behaviour of Drosophila melanogaster was analysed to determine the behavioural mechanisms by which larvae select pupation sites. Mature larvae of D. melanogaster perceive and react to humidity, light and the surface texture and consistency of the substrate. These stimuli induce in the larvae hydro- and photoresponses and burrowing, all of which are involved in larval pupation site choice. A selection scheme was applied to understand the genetic bases of preferences for pupation outside and inside the food cup. Pupation outside the cup on a dry substrate was dominant over pupation inside the cup. The results also suggested the presence of additive genes. Larvae of the lines selected to pupate outside the cup formed puparia away from the cup; those selected to pupate inside the cup were found near the food cup. Larvae of the F1 generation obtained by crossing the selected lines had a norm of reaction for prepupation behaviour which was greater than those of the parental lines. It is argued that heterozygosity permits a greater amplitude of modifications for this behaviour than homozygosity.

Larval digging behaviour of Drosophila melanogaster and the sibling species Drosophila pavani and Drosophila gaucha differs quantitatively. Digging activity increases with age. Crosses between four strains of D. melanogaster indicate dominance and heterosis for digging; some non-allelic interaction is also suggested. Larval locomotion of a line with low digging behaviour is lower than that exhibited by larvae of a line with high digging behaviour. Larvae of the low digging line form puparia away from the medium, while those of the high digging line select places close to the substrate. However, larvae of a separate digger strain (the Oregon R-C strain) show similar locomotor behaviour to that of larvae of another non-digger strain (the vestigial strain). It is suggested that, besides locomotion, photoresponse of larvae may also influence the dispersal pattern within food. Dominance and heterosis towards high digging suggest possible evolutionary importance for this behaviour.