Aggression towards shared enemies by heterospecific and conspecific cichlid fish neighbours

Abstract Successful territory defence is a prerequisite for reproduction across many taxa, and often highly sensitive to the actions of territorial neighbours. Nevertheless, to date, assessments of the significance of the behaviour of heterospecific neighbours have been infrequent and taxonomically restricted. In this field study, I examined the importance of both heterospecific and conspecific neighbours in a biparental fish, the convict cichlid, Amatitlania siquia. This was done by assessing the colonisation rates of vacant territories, the rates of aggression by the territory holders, and the overall rates of aggression towards intruders, in treatments that controlled the proximity of both neighbour types. Convict cichlid pairs colonised vacant nesting resources (territory locations) at similar rates independent of the proximity of heterospecific (moga, Hypsophrys nicaraguensis) or conspecific neighbours. However, a model of sympatric cichlid intruder was subjected to considerably higher overall levels of aggression when mogas were nearby. In contrast, the proximity of conspecifics did not have a significant effect on the overall aggression towards the intruder. These results suggest that previously demonstrated higher survival of convict cichlid broods in close proximity of mogas may be driven by aggression towards shared enemies. No conclusive evidence was found regarding whether mogas also influence convict cichlids’ investment into anti-intruder aggression: the results show a marginally non-significant trend, and a moderately large effect size, to the direction of a lower investment in mogas’, but not conspecifics’, proximity. More generally, heterospecific neighbours may provide protective benefits in a wider range of ecological settings than commonly considered

Male phenotype and resource type influence nesting behaviour in a fish

Abstract In many brood-rearing species, suitable nesting resources are needed for nest construction. Here, we used males of a small marine fish, the sand goby, Pomatoschistus minutus, to study the associations between the nest owner’s phenotype (i.e. body size), the characteristics of the nesting resource used for nest construction (i.e. resource size and shape) and nest-building behaviour (i.e. eagerness to build a nest and extent of nest elaboration). We found that male body size was associated with nesting resource size and resource architecture in the field, with the smallest males occupying small flat resources and the biggest males occupying large arched resources. In the laboratory, the type of resource occupied in the field had a limited effect on the level of nest elaboration, but not on other nesting behaviours. Large body size, in turn, was associated with preference for larger resources and, in some circumstances, also the level of nest elaboration. Body size did not affect the eagerness to initiate nest building. Furthermore, males chose arched nesting resources more often than those that were flat, and this preference was also reflected under a ’no-choice’ scenario, based on the time taken for males to initiate nest building. Overall, the results indicate that the importance of male size in nest building is context dependent, while nesting behaviours can also be affected by resource size, resource architecture and, under some circumstances, the nest builder’s experience with resource use

Context-dependent resource choice in a nest-building fish

Abstract When making decisions, individuals can be influenced by both the range of options available to them and intrinsic factors, such as their own body size or condition. The current understanding of the topic comes mostly from studies of foraging behaviour and mate choice, whereas other fitness-related decisions have been the subject of much less attention. Here, we investigated how the number of available options, along with body size and condition, affect the nesting resource choices of male sand gobies, Pomatoschistus minutus. The results show that resource choices were not affected by additional choice options (i.e. binary versus ternary choice situation) or the body condition of the chooser, whereas resource size, resource type (i.e. whether choices were between arched or flat resources) and body size did have an effect. In particular, while larger nesting resources were chosen more often in most situations, this pattern was stronger among larger males and when the resources had a flat, rather than arched, shape. Indeed, in the case of arched resources, the medium size category was more popular than the smaller and larger ones. Together, the results show that both intrinsic and extrinsic factors can influence important behavioural decisions over resource choice

Environmental variation promotes colour morph-specific behavioural differences in a cichlid fish

Abstract Colour polymorphisms are among the most striking examples of intraspecific variation. If vulnerability in a given habitat depends on body colour, heterogeneity in the environment may drive behavioural differences between differently coloured individuals. We tested this prediction in a colour-polymorphic fish species, the red devil, Amphilophus labiatus. In Amphilophus cichlids, ‘dark’ and ‘gold’ morphs have previously been linked to differences in morphology, aggressive behaviour and mate choice, but it is unknown whether the morphs also differ in other key behaviours, or whether any such differences are sensitive to environmental factors. By testing activity, boldness and exploration, our laboratory experiment provided moderate evidence for an environmental variable, substrate type, having colour morph-specific effects on behaviour: dark morph red devils explored their environment more extensively when the environmental background (substrate) was dark brown than when it was light coloured, whereas gold morph individuals did not differ in their behaviour in relation to substrate colour. These results show that environmentally driven behavioural differences may be context dependent and have a role in maintaining colour morph-specific behavioural strategies. Hence, the evolution of morphological traits, such as colour morphs, cannot be fully understood without considering the behavioural phenotypes that have coevolved with them in interaction with the environment

The duration of artificial light defines sexual signalling in the common glow-worm

Abstract Artificial light at night is increasing globally, interfering with both sensory ecology and temporal rhythms of organisms, from zooplankton to mammals. This interference can change the behaviour of the affected organisms, and hence compromise the viability of their populations. Limiting the use of artificial light may mitigate these negative effects. Accordingly, we investigated whether the duration of artificial light affects sexual signalling in female glow-worms, Lampyris noctiluca, which are flightless and attract flying males to mate by emitting glow that is interfered by light pollution. The study included three treatments: no artificial light (control), 15 min of artificial light, and 45 min of artificial light. The results show that females were more likely to cease glowing when the exposure to light was longer. Furthermore, small females were more likely to cease their glow, and responded faster to the light, than larger females. These findings suggest that glow-worms can react rapidly to anthropogenic changes in nocturnal light levels, and that prolonged periods of artificial light trigger females to stop sexual signalling. Thus, limiting the duration of artificial light can mitigate the adverse effects of light pollution on sexual signalling, highlighting the importance of such mitigation measures

When night never falls:female sexual signalling in a nocturnal insect along a latitudinal gradient

Abstract The environment can play an important role in animal communication by affecting signal transmission and detection. Variation in the signalling environment is expected to be especially pronounced in widely distributed species, potentially affecting how their signals are detected. Such environmental variability is presumably relevant for sedentary females of a nocturnal capital breeder, the European common glow-worm (Lampyris noctiluca), which produce green light during the night to attract flying males to mate. Being widely distributed in Europe, glow-worm populations are exposed to both rapidly descending, darker summer nights in the south, and slowly dimming, brighter summer nights further north, with the latter potentially posing challenges to the visibility of the female glow. To test how female signalling is affected by latitude, we sampled glowing females during summer nights along a latitudinal gradient in Finland, Northern Europe, and used a novel apparatus to measure the intensity and peak wavelength (hue/colour) of their glow. Surprisingly, females at higher latitudes, similar to those at lower latitudes, were commonly glowing during the brightest (and hence the shortest) nights of the year. Females also glowed brighter in more northern areas, partly due to their larger body size, whereas the colour of their glow was not associated with latitude. Since females glow even during midsummer, independent of latitude, the increase in glow intensity at higher latitudes presumably serves to maintain signal visibility in brighter signalling conditions. Overall, these findings highlight the influence of environmental conditions on the evolution of sexual signals, especially in the context of species distribution range

Size, more than colour, drives dyadic interactions in sub-adults of a colour polymorphic cichlid

Abstract Social and aggressive behaviours often affect the fitness of multiple interacting individuals simultaneously. Here, we assessed dyadic interactions in a colour-polymorphic cichlid fish, the red devil, Amphilophus labiatus. We found that sub-adult red devil pairs of smaller body size interacted more, and were more aggressive towards each other, than pairs comprising larger individuals. Interactions did not significantly differ between colour morphs, i.e. between dark, gold and heterotypic pairs. Interestingly, within a broad range of parameters, an automated measure of time that the two fish spent in close proximity was an accurate proxy for their level of aggression, as measured by an observer from video recordings. These results show that, between sub-adult red devils, (aggressive) interactions significantly depend on body size, but not colour morph, of the interacting individuals. In addition, the results support the use of automated data-gathering approaches as an appropriate tool for studies of aggression