Sibling association among schooling toad tadpoles: field evidence and implications

Grouping rule in tadpole: is quantity more or size assortment more important?

The ability to perceive group size and discriminate the ontogeny of conspecifics would play a crucial role in the grouping behavior of animals. However, the relative importance of numerical quantity and size-assortative preferences in shaping grouping rules remains poorly understood. In this study, I examined the responses of Miyako toad (Bufo gargarizans miyakonis) tadpoles to number quantity and size discrimination by choice tests at different ontogenetic stages (small, medium, and large). The results revealed that small-sized tadpoles in early developmental stages significantly preferred larger numbers (4) compared to smaller ones (1). However, this preference was not observed in later developmental stages (medium and large). And interestingly, when there was no quantity bias, size discrimination was not observed in tadpoles, irrespective of their ontogeny. These findings suggest that Miyako toad tadpoles discern quantity, i.e., the number of conspecifics, but exhibit ontogeny-dependent utilization of this ability. Understanding the interplay between numerical quantity and size-assortative preferences in grouping behavior will provide esteemed insights into the adaptive value of number sense in vertebrates and shed light on evolutionary processes.

Plasticity for the kin and conspecific preferences in the frog tadpoles (Rana ornativentris)

In vertebrates, little is known of kin recognition systems and their plasticity. Even in well-studied anuran larvae (tadpoles), the determinants and effects of prior experience have not been clarified. This study evaluates the plasticity of kin and conspecific discrimination in tadpoles of the Japanese montane brown frog Rana ornativentris. We raised tadpoles under two different sibship conditions: the pure line, comprising only siblings, and the mixed line, comprising both siblings and non-siblings. The association preference by a subject tadpole to unfamiliar ("stimulus") tadpoles was assessed through binary-choice tests using a 2 × 2 × 2 factorial design among each kinship line (pure and mix), subject ontogeny/size (early stage/small and late-stage/large), and stimuli ontogeny/size. Contrary to our expectations, kin preference was confirmed only in early developmental small tadpoles from mixed line, and only with a small stimulus. Furthermore, tadpoles from mixed line did not exhibit size preference for unrelated conspecifics. These results suggest that different prior associations have modulated kin templates along tadpole ontogeny and that the presence of non-kin would enhance the learning of kin/non-kin. This study provides the first example that plasticity of kin recognition affects not only kin-biased association but also conspecific recognition along ontogeny in tadpoles.

Lurking in the depth: Pond depth predicts microhabitat selection by Rhinella icterica (Anura: Bufonidae) tadpoles at two different sampling scales

Habitat selection has long been a central theme in ecology and has historically considered both physiological responses and ecological factors affecting species establishment. Investigating habitat selection patterns at different scales can provide important information on the relative roles of the environmental factors influencing the organisms’ abilities to use their surrounding habitat. This work aimed at investigating which environmental factors determine habitat selection by Rhinella icterica tadpoles, and also took the opportunity to investigate how the scale in which tadpoles and environmental data are sampled might influence the habitat selection results. A total of 2.240 tadpoles were counted in the whole sampling area, and while substrate cover and depth were the variables that better explained the abundance of tadpoles at the larger scale (plot level), depth and water turbidity better explained tadpoles’ abundance at the smaller scale (subplot level). The results suggest that avoiding predation by matching the background color is a likely process explaining tadpoles’ occupancy at both scales. Depth is known to influence tadpole habitat use in the tropics, and although its combination with turbidity and substrate cover varied between scales, our study suggests that sampling at different scales might not affect the inferred ecological processes driving habitat selection. This information might also be useful to predict tadpoles’ responses to micro-environmental perturbations and help in guiding the choice of parameters that should be taken into account when analyzing the effects of habitat degradation in Atlantic Forest amphibian populations.

Safety Bubbles: A Review of the Proposed Functions of Froth Nesting among Anuran Amphibians

The adults of several anuran amphibian species deposit their eggs externally in mucus secretions that are purposely aerated to produce a froth nest. This type of clutch structure has evolved independently several times in this group and has been proposed to serve a variety and often simultaneous adaptive functions associated with protecting offspring from sub-optimal conditions during embryogenesis and later stages after hatching has occurred. These functions range from buffering offspring from sub-optimal temperatures and desiccation, to defending against predation and improving oxygenation. This versatility has likely helped facilitate the reduced reliance of egg development on water and thus the penetration of anurans into environments where permanent aquatic systems are not always available. In this paper, I review the hypothesised functions of the anuran froth nest as a mucus-based solution to the environmental challenges offspring face during development, with consideration of the functions of froth nest breakdown and communal froth nesting, as well.

Attraction to conspecifcs in Rhinella icterica and R. ornata tadpoles (Anura: Bufonidae)

Abstract: Tadpoles are able to perceive and discriminate signals from environment and they may use this ability in behaviors and ecological processes. Recognition mechanisms may be involved in schooling by means of attraction among individuals, characterizing a social process. By means of laboratory experiments the present study investigated the presence or absence of attraction to conspecifics in tadpoles of Rhinella icterica and R. ornata, two sympatric species from the Atlantic Forest of southeastern Brazil. We collected eggs of these two species in the field and reared them in laboratory according to two different methods (isolated or in groups of siblings). Tadpoles were submitted to experiments of choice between conspecifics, heterospecifics, and an empty compartment. Rhinella icterica tadpoles preferred to associate with conspecifics rather than R. ornata tadpoles, and we verified this is an innate behavior. Rhinella ornata tadpoles failed to discriminate between conspecifics and R. icterica tadpoles. When submitted to choice between a group of tadpoles of the other species and an empty compartment, R. icterica tadpoles presented random distribution, while R. ornata tadpoles preferred to associate with heterospecifics. Our results indicate R. icterica tadpoles have preference to associate with conspecifics, while R. ornata tadpoles may school indiscriminately. This study contributes for a better understanding of larval anuran social behavior.

Adaptation to public goods cheats in Pseudomonas aeruginosa

Cooperation in nature is ubiquitous, but is susceptible to social cheats who pay little or no cost of cooperation yet reap the benefits. The effect such cheats have on reducing population productivity suggests that there is selection for cooperators to mitigate the adverse effects of cheats. While mechanisms have been elucidated for scenarios involving a direct association between producer and cooperative product, it is less clear how cooperators may suppress cheating in an anonymous public goods scenario, where cheats cannot be directly identified. Here, we investigate the real-time evolutionary response of cooperators to cheats when cooperation is mediated by a diffusible public good: the production of iron-scavenging siderophores by Pseudomonas aeruginosa. We find that siderophore producers evolved in the presence of a high frequency of non-producing cheats were fitter in the presence of cheats, at no obvious cost to population productivity. A novel morphotype independently evolved and reached higher frequencies in cheat-adapted versus control populations, exhibiting reduced siderophore production but increased production of pyocyanin—an extracellular toxin that can also increase the availability of soluble iron. This suggests that cooperators may have mitigated the negative effects of cheats by downregulating siderophore production and upregulating an alternative iron-acquisition public good. More generally, the study emphasizes that cooperating organisms can rapidly adapt to the presence of anonymous cheats without necessarily incurring fitness costs in the environment they evolve in.

"KIN RECOGNITION" AMONG SPADEFOOT TOAD TADPOLES: A SIDE-EFFECT OF HABITAT SELECTION?

Many animals modify their behavior toward unfamiliar conspecifics as a function of their genetic relatedness. A fundamental problem of any kin recognition study is determining what is being recognized and why. For anuran tadpoles, the predominant view is that associating with relatives is kin-selected because these relatives may thereby accrue benefits through increased growth or predation avoidance. An alternative view is that kin associations are simply a side-effect of habitat selection and thus do not represent attempts to identify kin per se. In the laboratory, spadefoot toad tadpoles (Scaphiopus multiplicatus) preferentially associated with unfamiliar siblings over unfamiliar nonsiblings, as do other anurans. However, same age tadpoles also were more likely to orient toward unfamiliar nonsiblings reared on the same food (familiar food) than toward unfamiliar siblings that were reared on unfamiliar food. These results, together with the results of previous tadpole kin recognition studies, suggest that tadpoles orient toward cues learned early in ontogeny, regardless of the cues' source. Tadpoles that preferentially associated with cues learned from their environment at birth would tend to be philopatric. Censuses of 14 natural ponds revealed that tadpole density remained greatest near oviposition sites until four days before metamorphosis. Tadpole philopatry may be advantageous: tadpoles restricted to their natal site had greater growth and survivorship than did their siblings restricted to randomly selected sites elsewhere within the same pond. Thus kin affiliative tendency observed in the laboratory in this and perhaps other species of anurans may be a byproduct of habitat selection. Since kin discrimination in animals is most commonly assayed as orientation toward kin, it follows that many examples of "kin recognition" may not represent true attempts to identify kin as such, but rather may reflect some other recognition system that is under entirely different selective pressures.

Does relatedness influence the intensity of competition in Bufo gargarizans minshanicus tadpoles?

Kin selection theory predicts that mechanisms should evolve to reduce kin competition when this maximizes inclusive fitness. In this study, we tested these predictions by investigating the effects of relatedness on fitness-related metamorphic traits (e.g., length of larval period, size at metamorphosis, body condition and survival rate). We did this in a laboratory experiment by exposing individuals of Bufo gargarizans minshanicus to competition with full-sibling or non-sibling larvae. Although tadpoles seemed to grow slightly better in environments when their competition consisted of full-siblings than when their competitors consisted of non-siblings, these effects of relatedness on the growth and development were not significant. Therefore, we suggest that interference competition may be equally intense in in full-sibling and non-sibling groups.

Making friends: social attraction in larval green and golden bell frogs, Litoria aurea

Socio-ecological models combine environmental and social factors to explain the formation of animal groups. In anurans, tadpole aggregations have been reported in numerous species, but the factors driving this behaviour remain unclear. We conducted controlled choice experiments in the lab to determine whether green and golden bell frog (Litoria aurea) tadpoles are directly attracted to conspecifics (social factors) in the absence of environmental cues. Using repeated measures, we found that individual tadpoles strongly preferred associating with conspecifics compared to being alone. Furthermore, this preference was body size dependent, and associating tadpoles were significantly smaller than non-associating tadpoles. We suggest that small tadpoles are more vulnerable to predation and therefore more likely to form aggregations as an anti-predator behaviour. We demonstrate that tadpoles present an ideal model system for investigating how social and ecological factors influence group formation in vertebrates.

Problems of kin recognition

Behavioural ecologists have long assumed that animals discriminate between their kin and non-kin, but paid little attention to how animals recognize their relatives. Although the first papers on kin recognition mechanisms appeared barely 10 years ago, studies now appear frequently in journals of animal behaviour. Initial findings reveal that kin recognition abilities are surprisingly well-distributed throughout the animal kingdom. Yet an understanding of the evolutionary and ecological significance of these abilities demands further analyses of the components of kin recognition mechanisms and the social contexts in which they are expressed. Many controversies and unresolved issues remain, and experimental approaches to these problems promise to continue making kin recognition an important, rapidly moving discipline within behavioural ecology.

Kin discrimination and altruism in the larvae of a solitary insect

Kin selection theory predicts altruism between related individuals, which requires the ability to recognize kin from non-kin. In insects, kin discrimination associated with altruistic behaviour is well-known in clonal and social species but in very few solitary insects. Here, we report that the solitary larvae of a non-social insect Aleochara bilineata Gyll. (Coleoptera; Staphylinidae) show kin discrimination and sibling-directed altruistic behaviour. Larvae superparasitize more frequently the hosts parasitized by non-kin individuals than those hosts parasitized by siblings. Kin discrimination probably occurs by self-referent phenotype matching, where an individual compares its own phenotype with that of a non-familiar related individual, a mechanism rarely demonstrated in animals. The label used to recognize kin from non-kin corresponds to substances contained in the plug placed on the hosts by the resident larvae during the parasitization process. Kin competition induced by a limited larval dispersion may have favoured the evolution of kin recognition in this solitary species.

Dominance in Vertebrate Broods and Litters

Drawing on the concepts and theory of dominance in adult vertebrates, this article categorizes the relationships of dominance between infant siblings, identifies the behavioral mechanisms that give rise to those relationships, and proposes a model to explain their evolution. Dominance relationships in avian broods can be classified according to the agonistic roles of dominants and subordinates as "aggression-submission," "aggression-resistance," "aggression-aggression," "aggression-avoidance," "rotating dominance," and "flock dominance." These relationships differ mainly in the submissiveness/pugnacity of subordinates, which is pivotal, and in the specificity/generality of the learning processes that underlie them. As in the dominance hierarchies of adult vertebrates, agonistic roles are engendered and maintained by several mechanisms, including differential fighting ability, assessment, trained winning and losing (especially in altricial species), learned individual relationships (especially in precocial species), site-specific learning, and probably group-level effects. An evolutionary framework in which the species-typical dominance relationship is determined by feeding mode, confinement, cost of subordination, and capacity for individual recognition, can be extended to mammalian litters and account for the aggression-submission and aggression-resistance observed in distinct populations of spotted hyenas and the "site-specific dominance" (teat ownership) of some pigs, felids, and hyraxes. Little is known about agonism in the litters of other mammals or broods of poikilotherms, but some species of fish and crocodilians have the potential for dominance among broodmates.

Size-related performance variation in the wood frog (Rana sylvatica) tadpole tactile-stimulated startle response

I described the initial response of the Rana sylvatica LeConte, 1825 tadpole to predator contact, that is, the tactile-stimulated startle response (TSR). Because tadpole survival from predation increases with tadpole size and with exposure to chemical predator cues during development, I anticipated that TSR performance would vary accordingly among tadpoles. Startle responses were stimulated in a laboratory setting and filmed using high-speed video. This method allowed analysis of performance at fine spatial and temporal scales. Maximum acceleration performance increased with tadpole length, as did cumulative distance covered after the first 0.016 s of the response. In contrast, the cumulative distance covered during the initial instants of the response did not depend on tadpole size. Exposure to a predator cue (odor of the dragonfly naiad Anax junius (Drury, 1773)) during development had no effect on tadpole morphology. Predator-cue exposure negatively affected cumulative distance traveled after the first 0.072 s of the startle response. I concluded that size-dependent variation in performance of the TSR may partially explain differential survival of tadpoles, but there was no evidence that exposure to this predator cue increased TSR performance.

The ontogeny of kin recognition in tadpoles of the toad Bufo melanostictus (Anura; bufonidae)

The ontogeny of kin recognition and influence of social environment on the development of kin recognition behaviour was experimentally investigated in tadpoles of Bufo melanostictus that lived in aggregations and showed low larval dispersion. Embryos and tadpoles of the toad were reared as (i) kin only, (ii) with kin and non-kin (separated by a mesh screen), and (iii) in isolation. They were tested for the ability to discriminate between (i) familiar siblings and unfamiliar non-siblings, (ii) familiar siblings and familiar non-siblings and, (iii) unfamiliar siblings and unfamiliar non-siblings. All tadpoles were fed on boiled spinach before conducting trials. Preference of test tadpoles to associate near the end compartments whether empty or containing members of specific stimulus groups was assessed using a rectangular choice tank. When tested in tanks with empty end compartments, the test tadpoles showed random distribution and thus no bias for the apparatus or the procedure. In the presence of kin/non-kin in the end compartments a significantly greater number of test tadpoles spent the majority of the time near familiar or unfamiliar kin rather than near familiar or unfamiliar non-kin. Kin discrimination ability persisted throughout larval development. Familiarity with siblings is not required for discriminating kin from non-kin, and kin discrimination ability is not modified following exposure to non-kin. Also, involvement of dietary cues is unlikely to be the prime mechanism of kin recognition in B. melanostictus unlike in some other anurans.

Kin discrimination in juvenile brook trout (Salvelinus fontinalis) and the effect of odour concentration on kin preferences

Kin discrimination abilities have been demonstrated in juveniles of many salmonid species. In this study, two experiments were conducted to determine: (i) if juvenile brook trout (Salvelinus fontinalis) have the ability to discriminate kin based on chemosensory cues and (ii) the effect that odour concentration has on an individual's preference. In the first experiment, individuals spent more time in water conditioned by kin than in water conditioned by non-kin, indicating that juvenile brook trout have the ability to discriminate kin based on chemosensory cues. Individuals in the second experiment based preferences on both concentration and kinship. When odour concentrations were equal, individuals preferred water conditioned by kin over that conditioned by non-kin. However, if given a choice between high and low concentrations, individuals preferred the high concentration independent of kinship. Individuals may perceive the various odour concentrations as an indicator of shoal size and base preferences on these differences.

Sibling recognition in the beaver: a field test for phenotype matching

The hypothesis of kin recognition by phenotype matching predicts that relatives can be identified without previous contact, and/or that cues used for recognition can be learned indirectly from a third but related individual. This hypothesis was tested in the field using 22 beaver, Castor canadensisfamilies. Individually identifiable beavers were provided with a two-way choice between two experimental scent mounds, one of which was scented with the anal gland secretion (AGS) from an unfamiliar sibling of the test subjects, the other with AGS from an unfamiliar non-relative. Beavers showed less strong territorial responses to AGS from their siblings than to that from non-relatives. The mates of the test subjects, which were not related to, or familiar with, either of the AGS donors, also responded less strongly to the AGS from their mates' siblings than to that from other unfamiliar non-relatives. This discrimination was not shown when castoreum samples were tested instead of AGS. Therefore, it was concluded that (1) information about kinship in the beaver is coded in the AGS but not in the castoreum, (2) the mechanism of phenotype matching is used in beaver sibling recognition, and (3) the cue used in phenotype matching can be learned and used for recognition of related individuals by an unrelated individual.1997The Association for the Study of Animal Behaviour

Development of anuran locomotion: ethological and neurophysiological considerations

There are dramatic quantitative and qualitative differences in the locomotor behavior of larval and juvenile frogs. Larvae (tadpoles) are primarily herbivourous and rely heavily on locomotion via undulations to acquire food and avoid predation. After metamorphosis, juvenile frogs adopt a carnivorous lifestyle and capture prey and avoid predators by remaining motionless in a place of concealment. When they must move, frogs locomote by means of ballistic hops or by more conventional walking. However, locomotion of both tadpoles and frogs can be considered of two fundamental functional types: (a) startle and escape; and (b) sustained locomotion. Neural mechanisms underlying startle responses and sustained locomotion in larvae and juveniles are described and possible ontogenetic relationships those behaviors are proposed. The role of different parts of the nervous system in the ontogeny of locomotion, as well as nonneuronal factors, are described. Results show that the transition from tadpole-like behavior to frog-like behavior is not a simple function of maturation of central locomotor controls. Rather, it results from a complex interaction of central nervous system maturation, morphological change, and a change in habitat preference. Examples of similar multidimensional control of behavioral ontogeny in other species are described, and it is argued that to understand the ontogeny of behavior, one must investigate contributions made at all levels, from the neuronal to the environmental.