Cooperative breeders feature the highest level of social complexity among vertebrates. Environmental constraints foster the evolution of this form of social organization, selecting for both well-developed social and ecological competences. Cooperative breeders pursue one of two alternative social trajectories: delaying reproduction to care for the offspring of dominant breeders or dispersing early to breed independently. It is yet unclear which ecological and social triggers determine the choice between these alternatives and whether diverging developmental trajectories exist in cooperative vertebrates predisposing them to dispersal or philopatry. Here we experimentally reared juveniles of cooperatively breeding cichlid fish by varying the social environment and simulated predation threat in a two-by-two factorial long-term experiment. First, we show that individuals develop specialized behavioral competences, originating already in the early postnatal phase. Second, these specializations predisposed individuals to pursue different developmental trajectories and either to disperse early or to extend philopatry in adulthood. Thus, our results contrast with the proposition that social specializations in early ontogeny should be restricted to eusocial species. Importantly, social and ecological triggers were both required for the generation of divergent life histories. Our results thus confirm recent predictions from theoretical models that organisms should combine relevant information from different environmental cues to develop integrated phenotypes.

Investigating the role of visual information in animal communication often involves the experimental presentation of live stimuli, mirrors, dummies, still images, video recordings or computer animations. In recent years computer animations have received increased attention, as this technology allows the presentation of moving stimuli that exhibit a fully standardized behaviour. However, whether simple animated 2D-still images of conspecific and heterospecific stimulus animals can elicit detailed behavioural responses in test animals is unclear thus far. In this study we validate a simple method to generate animated still images using PowerPoint presentations as an experimental tool. We studied context-specific behaviour directed towards conspecifics and heterospecifics, using the cooperatively breeding cichlid Neolamprologus pulcher as model species. N. pulcher did not only differentiate between images of conspecifics, predators and herbivorous fish, but they also showed adequate behavioural responses towards the respective stimulus images as well as towards stimulus individuals of different sizes. Our results indicate that even simple animated still images, which can be produced with minimal technical effort at very low costs, can be used to study detailed behavioural responses towards social and predatory challenges. Thus, this technique opens up intriguing possibilities to manipulate single or multiple visual features of the presented animals by simple digital image-editing and to study their relative importance to the observing fish. We hope to encourage further studies to use animated images as a powerful research tool in behavioural and evolutionary studies.

Theory predicts that animals should adjust their escape responses to the perceived predation risk. The information animals obtain about potential predation risk may differ qualitatively depending on the sensory modality by which a cue is perceived. For instance, olfactory cues may reveal better information about the presence or absence of threats, whereas visual information can reliably transmit the position and potential attack distance of a predator. While this suggests a differential use of information perceived through the two sensory channels, the relative importance of visual vs. olfactory cues when distinguishing between different predation threats is still poorly understood. Therefore, we exposed individuals of the cooperatively breeding cichlid Neolamprologus pulcher to a standardized threat stimulus combined with either predator or non-predator cues presented either visually or chemically. We predicted that flight responses towards a threat stimulus are more pronounced if cues of dangerous rather than harmless heterospecifics are presented and that N. pulcher, being an aquatic species, relies more on olfaction when discriminating between dangerous and harmless heterospecifics. N. pulcher responded faster to the threat stimulus, reached a refuge faster and entered a refuge more likely when predator cues were perceived. Unexpectedly, the sensory modality used to perceive the cues did not affect the escape response or the duration of the recovery phase. This suggests that N. pulcher are able to discriminate heterospecific cues with similar acuity when using vision or olfaction. We discuss that this ability may be advantageous in aquatic environments where the visibility conditions strongly vary over time.Significance statementThe ability to rapidly discriminate between dangerous predators and harmless heterospecifics is crucial for the survival of prey animals. In seasonally fluctuating environment, sensory conditions may change over the year and may make the use of multiple sensory modalities for heterospecific discrimination highly beneficial. Here we compared the efficacy of visual and olfactory senses in the discrimination ability of the cooperatively breeding cichlid Neolamprologus pulcher. We presented individual fish with visual or olfactory cues of predators or harmless heterospecifics and recorded their flight response. When exposed to predator cues, individuals responded faster, reached a refuge faster and were more likely to enter the refuge. Unexpectedly, the olfactory and visual senses seemed to be equally efficient in this discrimination task, suggesting that seasonal variation of water conditions experienced by N. pulcher may necessitate the use of multiple sensory channels for the same task.Electronic supplementary materialThe online version of this article (10.1007/s00265-017-2371-8) contains supplementary material, which is available to authorized users.

The megophryid frogs Leptobrachella brevicrus, Leptolalax dringi and Megophrys dringi are species exclusively known from highly localised areas in isolated mountain ranges on Borneo. The tadpoles and adults in this study were collected at the shared type locality for the three species in Gunung Mulu National Park, Sarawak, Malaysia (Borneo). The species identities of larvae were determined via comparison to syntopic adults using DNA barcoding techniques based on partial 16S rRNA mitochondrial gene sequences. The genetic data supported the status of the three taxa as valid species. Descriptions of colouration in life and after preservation, external morphological features, morphometric measurements and ecological notes in comparison to congeneric species are supplied. The tadpoles of L. brevicrus and L. dringi show similar adaptations to a fossorial lifestyle. These include an elongated, vermiform body, a relatively long tail and small eyes. Both were found in the gravel beds of a small mountain stream. In contrast, the larvae of M. dringi are adapted to occupying and feeding at the surface of pools within the stream.

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