Bruce Waldman

Mechanisms of kin recognition

Although kin recognition mechanisms are necessary neither for the operation of kin selection nor for optimal mate selection (e.g. inbreeding avoidance), once established, such mechanisms may accelerate the evolution of kin-directed behaviors. Aside from spatially-based recognition, in which organisms adjust their behavior principally in response to their immediate location, several behavioral mechanisms originally suggested by Hamilton recently have generated discussion and controversy. Familiar kin can be identified individually, but individual recognition mechanisms alone cannot serve to distinguish between closely and more distantly related kin, or to identify novel relatives. These kin can be identified through group recognition mechanisms that evaluate the extent of trait overlap among individuals to determine their probable genetic relatedness. Precisely whom an organism recognizes as kin using either type of mechanism may be dependent on its past social experience. Individual recognition permits discrimination of previously encountered conspecifics, whereas group recognition generally leads to discrimination of individuals sharing traits with previously encountered conspecifics. Individual and group recognition mechanisms are not mutually exclusive, and they may operate concurrently. Furthermore, they are not distinct, separable processes. Mistaken individual identifications become more likely as conspecifics show increasing phenotypic resemblance, and hence kin discrimination can result directly from individual recognition mechanisms. The extent to which kin are identified depends on a criterion rule which may fluctuate in response to social, spatial, and temporal factors. When favored by natural selection, kin recognition may be facilitated by the process of stimulus generalization, as trait matching is achieved within wider tolerance ranges. But such generalization may occur even in the absence of selection per se . Recognition effected through the action of hypothetical “recognition alleles” does not constitute a logical alternative to individual or group kin recognition mechanisms. In common with those processes, recognition allels must operate by the effective matching of phenotypes. Unlike kin recognition mechanisms, which assess similarity by generalized phenotypic comparisons, the phenotype compared by a recognition allele (or linkage group) is that it itself generates, leading to the possibility of intragenomic conflict. As suggested by Hamilton, alleles might be expected to induce their bearers to favor behaviorally conspecifics that share thier copies, regardless of the overall genetic relatedness of those conspecifics. Hence, recognition alleles, if they exist, would not invariably lead to kin identifications. Moreover, such alleles need not act in a manner that necessarily excludes learning. Through inbreeding experiments, a genetic component to the labels that elicit kin recognition has been demonstrated in some invertebrates. Genetically determined kin recognition templates, with which the labels are compared, have yet to be established. A “genetic recognition system” cannot be safely inferred when experiments fail to demonstrate experiential effects on recognition abilities. Kin recognition mechanisms can be characterized through detailed examination of the ontogenetic and sensory processes underlying recognition abilities, and of the ecological and social contexts in which kin-directed behaviors are expressed.

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.

Functional analyses of nanoparticle toxicity: A comparative study of the effects of TiO2 and Ag on tomatoes (Lycopersicon esculentum)

Engineered nanoparticles (NPs), increasingly used in industry, enter and migrate through biological ecosystems. NPs may create some acute toxicity, but their overall effects on living organisms remain largely unknown. In particular, the behavior of NPs in natural conditions and their consequent ecological effects are still poorly understood. In this study, we developed methods to test the phytotoxicity of two distinctly different NPs, one aerosol (nano-TiO2), and the other colloidal silver (AgNP), by specifically considering their tendencies to agglomerate and form precipitates. First we examined effects of these NPs on germination and root elongation. While exposure to neither of these NPs resulted in acute toxicity on germination, silver NPs caused significantly decreased root elongation at every concentration we tested. We found that the hydrodynamic diameters of AgNPs were much smaller than those of nano-TiO2, which induced higher uptake and phytotoxicity. Based on the agglomeration behavior of the NPs, greenhouse trials were run using commercial soil, for nano-TiO2, and Hoaglands solution, for AgNP. Phytotoxicity of silver NPs in the mature plants was demonstrated by lower chlorophyll contents, higher superoxide dismutase activity and less fruit productivity, while nano-TiO2 resulted in higher superoxide dismutase activity at the highest concentration (5000mg/kg). Both nano-TiO2 and AgNPs were taken up into plant stems, leaves and fruits. Our results suggest that further studies of the ecological effects of nanoparticles and steps to mitigate appropriate management strategies are required.

Kin recognition in anuran amphibians

Abstract Anuran amphibians have emerged as model vertebrates for the study of kin recognition mechanisms. Larvae of most species reported to date discriminate between kin and non-kin, but anuran kin recognition systems show substantial interspecific variability. The ability to discriminate between kin and non-kin incorporates some form of learning in most, if not all, anuran species studied. Kin recognize one another through chemical cues which may incorporate environmental, genetic and maternal factors. The development of kin recognition is influenced by the rearing environment in some species, but in others, social factors have little effect. Kin recognition is context-dependent, however, and the failure to discriminate between kin and non-kin in laboratory tests may reflect artificial testing circumstances rather than differences in kin recognition abilities. Kin recognition mechanisms may have been selected because they enhance opportunities for cooperation among close relatives, but also might result incidentally from other life history processes. Larval growth and maturation may be accelerated when tadpoles recognize and preferentially associate with siblings. Moreover, kin recognition abilities sometimes are retained through metamorphosis. In natural populations, toads rarely mate with their siblings though close kin are readily accessible as mates. These findings suggest that kin recognition may facilitate optimal outbreeding.

Quantitative and Developmental Analyses of the Alarm Reaction in the Zebra Danio, Brachydanio rerio

The response of Brachydanio rerio in aquaria to alarm substance extracted from injured conspecifics was analyzed over 180 min periods. Three indices were devised to facilitate description: 1) an index of the fishs vertical distribution, 2) an index of their horizontal distribution and 3) a clumping index. In response to alarm substance, fish moved toward the substrate and clumped, but showed no consistent change in horizontal distribution. The magnitude of the response, as measured by the time for recovery to pretesting distributions, became greater with increasing pheromone concentration. The fishs response was not affected by a preceding test, but longer term conditioning effects are possible. Experiments on the development of the response during ontogeny showed that naive fry first react to alarm substance 48-52 days after hatching, at least 17 days after the substance is contained in their skin. The method of behavioral assay described here can detect subtle changes in the alarm response, and thus may be useful in future studies of alarm behavior.

Embryonic olfactory learning in frogs

We examined the effect of embryonic olfactory experiences on behaviour after hatching in two species of anuran amphibians, Rana temporaria and Rana sylvatica. Odorants (orange and citral) injected into the egg were “learned” by the embryo and subsequently preferred by tadpoles after hatching. The observed preferences were specific to the odours experienced prior to hatching, and tadpoles discriminated between the odour experienced as embryos and a novel odour. The acquired preference was maintained after metamorphosis for those individuals that exhibited a preference as tadpoles. Preferences of tadpoles were also influenced “naturally” by odours present in the water surrounding the developing embryos. The experimentally induced olfactory preferences did not appear to influence the exhibition of sibling recognition abilities. The study represents the first demonstration of “embryonic” learning in amphibians, and the functions and importance of early olfactory learning for amphibians are discussed.

Olfactory basis of kin recognition in toad tadpoles

Summary1.Larvae of the American toad (Bufo americanus) preferentially associate with their siblings in laboratory tests, suggesting that they can recognize kin. The sensory basis of their kin recognition abilities was investigated by measuring the responses of individuals in a Y-maze to waterborne cues emanating from their siblings and from nonsiblings.2.When simultaneously presented with water flowing from two containers, each holding members of a different sibling group, test subjects spent significantly more time oriented toward their siblings than toward non-siblings. Similar results were obtained when the stimulus water was first passed through intermediary reservoirs. Hence, kinship cues are unlikely to be acoustic or vibratory stimuli perceived by the auditory or lateral line systems.3.Tadpoles whose external nares were blocked with a gelatinous paste did not behaviorally discriminate between water flowing from siblings and that flowing from non-siblings. Retested after their nares were unplugged, these individuals oriented significantly toward their siblings, as did shamtreated test individuals.4.Stimulus water conditioned by sibling groups and then stored for 24–30 h failed to elicit a discrimination response, indicating that kinship cues released by tadpoles lose their effectiveness during this period. Signals with rapid fade-out times would probably be more efficient under natural conditions than those that persisted after individuals had moved.5.Test subjects simultaneously presented with water flowing from siblings and blank (dechlorinated tap) water showed no tendencies to discriminate between these stimuli. When individuals were exposed both to water from non-siblings and to blank water, however, they oriented significantly toward the blank water. Kin association may thus result in part from negative klinokinetic responses induced by contact with factors released by nonkin.6.Chemical cues released by tadpoles appear sufficient to communicate their kinship identity. These cues are probably perceived and processed by the main olfactory system. Kin recognition mechanisms may be further elucidated by chemical and neurophysiological analyses.

Adaptive significance of communal oviposition in wood frogs (Rana sylvatica)

Summary1.Wood frogs (Rana sylvatica) are one of the earliest anurans to breed in spring. Their breeding behavior is ‘explosive’, with most oviposition occurring within 2 to 6 days. Early breeding may reduce predation and ensure adequate developmental time for larvae, but it is accompanied by the risk of substantial egg mortality due to cold temperature.2.Males amplex females throughout breeding ponds, and pairs move toward a communal oviposition site. Females usually deposit eggs on submerged twigs or vegetation directly contiguous to other egg masses. Late breeders oviposit at the edge of the growing clump, thus surrounding the egg masses of earlier breeders.3.Egg masses in the center of a clump are insulated from thermal extremes in the surrounding water. Within a clump, central egg masses were warmer than peripheral egg masses, but egg masses at the edge of a clump were warmer than single egg masses deposited outside the clump.4.Central egg masses had significantly greater hatching success than peripheral egg masses. Central egg masses also had significantly more eggs than peripheral egg masses, suggesting that larger females obtained central sites.5.Because central egg masses have the greatest survivorship to hatching, wood frogs should be selected to breed early to obtain optimal oviposition sites. Breeding synchrony may result from this selection for early oviposition, with the ultimate limiting factors being how quickly frogs can emerge in the spring and when ice on ponds melts.

Genetic evidence for a high diversity and wide distribution of endemic strains of the pathogenic chytrid fungus Batrachochytrium dendrobatidis in wild Asian amphibians.

Population declines and extinctions of amphibians have been attributed to the chytrid fungus Batrachochytrium dendrobatidis (Bd), especially one globally emerging recombinant lineage (‘Bd‐GPL’). We used PCR assays that target the ribosomal internal transcribed spacer region (ITS) of Bd to determine the prevalence and genetic diversity of Bd in South Korea, where Bd is widely distributed but is not known to cause morbidity or mortality in wild populations. We isolated Korean Bd strains from native amphibians with low infection loads and compared them to known worldwide Bd strains using 19 polymorphic SNP and microsatellite loci. Bd prevalence ranged between 12.5 and 48.0%, in 11 of 17 native Korean species, and 24.7% in the introduced bullfrog Lithobates catesbeianus. Based on ITS sequence variation, 47 of the 50 identified Korean haplotypes formed a group closely associated with a native Brazilian Bd lineage, separated from the Bd‐GPL lineage. However, multilocus genotyping of three Korean Bd isolates revealed strong divergence from both Bd‐GPL and the native Brazilian Bd lineages. Thus, the ITS region resolves genotypes that diverge from Bd‐GPL but otherwise generates ambiguous phylogenies. Our results point to the presence of highly diversified endemic strains of Bd across Asian amphibian species. The rarity of Bd‐GPL‐associated haplotypes suggests that either this lineage was introduced into Korea only recently or Bd‐GPL has been outcompeted by native Bd strains. Our results highlight the need to consider possible complex interactions among native Bd lineages, Bd‐GPL and their associated amphibian hosts when assessing the spread and impact of Bd‐GPL on worldwide amphibian populations.

Kin recognition and sibling association among wood frog (Rana sylvatica) tadpoles

Summary1.Wood frog (Rana sylvatica) tadpoles, hatched from egg masses collected in the field, were reared either with siblings only or in mixed groups of eight sibships. Sibships were marked with vital stains, released in a laboratory test pool, and their spatial distributions recorded over a 4-day period.2.An analysis of nearest-neighbor distances suggests that tadpoles preferentially associated with familiar siblings over both familiar and unfamiliar non-siblings. Kinship preferences of R. sylvatica tadpoles, unlike those of other anurans that have been tested, thus appear largely unaffected by prior social experience.3.Tadpoles reared in mixed sibship groups preferentially associated with the siblings with which they were reared over unfamiliar siblings exposed to a different set of sibships. In contrast, tadpoles did not discriminate either between siblings reared in different baskets within the same mixed group tank, or between siblings housed in different singlesibship containers.4.Because R. sylvatica egg masses are usually deposited in communal clumps, an ability to recognize relatives not dependent on post-embryonic experience may have been selected. The possible adaptive significance of kin association among wood frog tadpoles is unknown; their schools probably do not represent kin groups, but larval distributions in natural ponds might reflect sibling association tendencies.5.Kin recognition “labels” of non-sibling R. sylvatica tadpoles reared together, like those of R. cascadae tadpoles similarly reared, may converge as a result of social interactions. R. sylvatica tadpoles, unlike R. cascadae tadpoles, retain an ability to discriminate between familiar siblings and familiar non-siblings; hence label transference may be incomplete.