Exploratory behaviour and transmission of information between the invasive guppy and native Mexican topminnows

The invasive twospot livebearer's biology, and its current and potential global distribution

Poeciliids are widely recognized as successful invaders, possessing traits associated with invasion success. Native to Central America and south-eastern Mexico, the twospot livebearer (Pseudoxiphophorus bimaculatus) is a species recently recognized as invasive in both Central and northern Mexico. Despite its invasive status, limited research exists on its invasion process and the potential threats it poses to native species. In this study, we conducted a comprehensive review of the current knowledge on the twospot livebearer and mapped its current and potential distribution worldwide. The twospot livebearer shares similar traits with other successful invaders within the same family. Notably, it exhibits high fecundity throughout the year and demonstrates resilience to highly polluted and oxygen-deprived water conditions. This fish serves as a host for several parasites, including generalists, and has been extensively translocated for commercial purposes. Recently, it has also been used for biocontrol within its native range. Apart from existing outside its native range, the twospot livebearer, under current climate conditions and if transported there, could readily colonize biodiversity hotspots in tropical zones worldwide, including the Caribbean Islands, the Horn of Africa, North of Madagascar Island, south-eastern Brazil, and others located in southern and eastern Asia. Given that this fish is highly plastic and our Species Distribution Model, we consider that all areas with a habitat suitability >0.2 should prevent its arrival and establishment. Our findings underscore the urgent need to recognize this species as a threat to freshwater native topminnows and prevent its introduction and spread.

Microhabitat conditions drive uncertainty of risk and shape neophobic responses in Trinidadian guppies, Poecilia reticulata

In response to uncertain risks, prey may rely on neophobic phenotypes to reduce the costs associated with the lack of information regarding local conditions. Neophobia has been shown to be driven by information reliability, ambient risk and predator diversity, all of which shape uncertainty of risk. We similarly expect environmental conditions to shape uncertainty by interfering with information availability. In order to test how environmental variables might shape neophobic responses in Trinidadian guppies (Poecilia reticulata), we conducted an in situ field experiment of two high-predation risk guppy populations designed to determine how the 'average' and 'variance' of several environmental factors might influence the neophobic response to novel predator models and/or novel foraging patches. Our results suggest neophobia is shaped by water velocity, microhabitat complexity, pool width and depth, as well as substrate diversity and heterogeneity. Moreover, we found differential effects of the 'average' and 'variance' environmental variables on food- and predator-related neophobia. Our study highlights that assessment of neophobic drivers should consider predation risk, various microhabitat conditions and neophobia being tested. Neophobic phenotypes are expected to increase the probability of prey survival and reproductive success (i.e. fitness), and are therefore likely linked to population health and species survival. Understanding the drivers and consequences of uncertainty of risk is an increasingly pressing issue, as ecological uncertainty increases with the combined effects of climate change, anthropogenic disturbances and invasive species.

Could non-native species boost their chances of invasion success by socializing with natives?

Most invasions start with the introduction of a few individuals and the majority fail to establish and become invasive populations. A possible explanation for this is that some species are subject to Allee effects-disadvantages of low densities-and fail to perform vital activities due to the low availability of conspecifics. We propose that 'facilitation' from native individuals to non-natives through heterospecific sociability could enhance chances of the latter establishing in novel environments by helping them avoid Allee effects and even reducing the minimum number of non-native individuals necessary to achieve the density for a viable population (the Allee effect threshold). There is evidence from experiments carried out with freshwater fish, snails, lizards, mussels and bird that supports the idea of heterospecific sociability between native and non-native species as a process to promote invasion success. We propose that to understand invasion success in social non-native species we need to investigate how they integrate into the recipient community. Furthermore, to manage them, it may be necessary to reduce population density not just below the Allee effect threshold but also to understand how natives could help them shift the conspecific Allee effect threshold to their benefit. This article is part of the theme issue 'Mixed-species groups and aggregations: shaping ecological and behavioural patterns and processes'.

Effect of a temperature gradient on the behaviour of an endangered Mexican topminnow and an invasive freshwater fish

Climate change and biological invasions are two of the major threats to biodiversity. They could act synergistically to the detriment of natives as non-native species may be more plastic and resilient when facing changing environments. The twoline skiffia (Skiffia bilineata) is an endangered Mexican topminnow that cohabits with invasive guppies (Poecilia reticulata) in some areas in central Mexico. Guppies have been found to take advantage from associating with the twoline skiffia and are considered partially responsible for the decline of its populations. Refuge use and exploratory behaviours are trade-offs between being safe from the unknown and the opportunity to explore novel areas in search for better resources or to disperse. The aim of this study is to investigate how a change in temperature affects the refuge use and exploratory behaviours for both species. We found that temperature affects the refuge use of twoline skiffias, and the swimming activity of both species. Skiffias explored the rock more than guppies regardless of the temperature scenario. Also, smaller fish spent more time performing exploratory behaviours than bigger ones. Our study is the first to test the effect of temperature on the refuge use and exploratory behaviour of a goodeid species, and our results contribute to the idea that some natives could be more affected by climate change than some invaders.

Sex, size and habitat complexity effects on emergence latency and latency to locate food of the invasive porthole livebearer (Poeciliopsis gracilis)

Biological invasions are considered the second major cause of plant, amphibian, reptile, and mammal loss worldwide. Like islands, freshwater ecosystems are especially susceptible to the negative impacts of invasions. The porthole livebearer (Poeciliopsis gracilis), recently identified as invasive in the Mexican Central Plateau, is increasing its populations and could impact freshwater ecosystems like its cousin species the guppy (Poecilia reticulata). Risk-taking behaviours, such as emergence latency, are recognised as key characteristics to invasion success and Poeciliid females can establish a viable population by themselves (due to their multiple paternity broods). We investigated the emergence latency and latency to locate food in simple and complex environments of porthole livebearers, including the effect of their size and sex. For both sexes, bigger fish emerge less times and take longer to do so, but females are faster to exit the refuge than males. We found no differences in porthole livebearer’s behaviour in complex or simple habitats, and no significant differences between sex, size or treatment in the time to locate food after exiting the refuge. Our results suggest that the benefit of faster emergence from the refuge in porthole livebearers in novel environments could be higher for females. We consider that porthole livebearer females being bolder could contribute to the invasion success of the species. Our study points at females and smaller fish as being the more likely to explore novel environments, which could contribute to understanding how the invasions by the porthole livebearer are driven.

No evidence that nest site choice in Pied Flycatchers is mediated by assessing the clutch size of a heterospecific, the Great Tit

Among species that use similar resources, an individual may benefit by observing and copying the behavioural decision of a heterospecific. We tested the hypothesis of heterospecific social learning in passerine birds, namely that a migrant species, the Pied Flycatcher Ficedula hypoleuca, uses external markings on the nest cavities of a resident species, the Great Tit Parus major, as cues when choosing a nest site. Others have suggested that prospecting flycatchers assess the clutch size of tit "demonstrators" by entering their nest boxes and, assuming that a large clutch indicates a high-quality individual, will copy the nest appearance of tits with large, but not small clutches. During a 4-year period in Norway, we designed a similar study but did not find that flycatchers based their nest choice on the clutch size of tits. Neither were there any relationships between clutch size of the tit and its laying date, incubation behaviour, or the number of eggs visible through nest material during egg-laying so Pied Flycatchers did not use these indirect cues to assess quality of the tutor. Filming of tit nests showed that prospecting flycatchers did not enter tit nest boxes to assess the content. Indeed, incubating female tits only left their nest boxes for short bouts of unpredictable duration so there was little opportunity for flycatchers to inspect the nest contents unnoticed. Our study calls into question the mechanism of using the content of tit nests as public information for choosing traits of nest sites based on external characteristics. We suggest that similar studies of nest site choice in relation to possible social information transfer be replicated more widely.

Con- and Heterospecific Shoaling Makes Invasive Guppies More Risk Taking

Invasive species are one of the greatest threats to biodiversity. Behavioral traits are recognized as key to promote individual’s survival in changing conditions. For social species being part of a group is key to carry out vital activities. Heterospecific social environments could provide exotic species with the opportunity to join groups and gain the advantages of being part of a larger population. Short latency to exit a refuge is a behavioral response that could be linked to invasion success as it increases the chances of individuals to locate food sources and other resources in novel environments. The guppy (Poecilia reticulata), a successful invader, has been found to take advantage of the presence of native species to reduce its refuge emergence latency and acquire information. The research was carried out in Mexico, we investigated the effect of heterospecific social contexts that include natives and other invasive viviparous fishes on guppies’ refuge emergence latency. We found that guppies’ emergence latency was shorter when accompanied by another guppy than when alone. Their latency was also shorter when with other invaders and when with native goodeids, but with one of the invaders (Pseudoxiphophorus bimaculatus) and with goodeids (Skiffia bilineata) latency reduction was not as high as when with conspecifics or with the invader Poecilia gracilis. Our experiment supports both the idea that already established invaders could provide benefits to new ones, and that native species also provide benefits but less than invaders. Increasing our knowledge about conspecific and heterospecific social interactions that could make an exotic species become invasive is key to assess the invasion risk of a community.

Consistent Behavioral Syndrome Across Seasons in an Invasive Freshwater Fish

Understanding the linkage between behavioral types and dispersal tendency has become a pressing issue in light of global change and biological invasions. Here, we explore whether dispersing individuals exhibit behavioral types that differ from those remaining in the source population. We investigated a feral population of guppies (Poecilia reticulata) that undergoes a yearly range shift cycle. Guppies are among the most widespread invasive species in the world, but in temperate regions these tropical fish can only survive in winter-warm freshwaters. Established in a thermally-altered stream in Germany, guppies are confined to a warm-water influx in winter, but can spread to peripheral parts as these become thermally accessible. We sampled fish from the source population and a winter-abandoned site in March, June and August. Fish were tested for boldness, sociability and activity involving open-field tests including interactions with a robotic social partner. Guppies differed consistently among each other in all three traits within each sample. Average trait expression in the source population differed across seasons, however, we could not detect differences between source and downstream population. Instead, all populations exhibited a remarkably stable behavioral syndrome between boldness and activity despite strong seasonal changes in water temperature and associated environmental factors. We conclude that random drift (opposed to personality-biased dispersal) is a more likely dispersal mode for guppies, at least in the investigated stream. In the face of fluctuating environments, guppies seem to be extremely effective in keeping behavioral expressions constant, which could help explain their successful invasion and adaptation to new and disturbed habitats.

'Stick with your own kind, or hang with the locals?' Implications of shoaling strategy for tropical reef fish on a range-expansion frontline

Range shifts of tropical marine species to temperate latitudes are predicted to increase as a consequence of climate change. To date, the research focus on climate-mediated range shifts has been predominately dealt with the physiological capacity of tropical species to cope with the thermal challenges imposed by temperate latitudes. Behavioural traits of individuals in the novel temperate environment have not previously been investigated, however, they are also likely to play a key role in determining the establishment success of individual species at the range-expansion forefront. The aim of this study was to investigate the effect of shoaling strategy on the performance of juvenile tropical reef fishes that recruit annually to temperate waters off the south east coast of Australia. Specifically, we compared body-size distributions and the seasonal decline in abundance through time of juvenile tropical fishes that shoaled with native temperate species ('mixed' shoals) to those that shoaled only with conspecifics (as would be the case in their tropical range). We found that shoaling with temperate native species benefitted juvenile tropical reef fishes, with individuals in 'mixed' shoals attaining larger body-sizes over the season than those in 'tropical-only' shoals. This benefit in terms of population body-size distributions was accompanied by greater social cohesion of 'mixed' shoals across the season. Our results highlight the impact that sociality and behavioural plasticity are likely to play in determining the impact on native fish communities of climate-induced range expansion of coral reef fishes.

Sociability between invasive guppies and native topminnows

The role of interspecific social interactions during species invasions may be more decisive than previously thought. Research has revealed that invasive fish improve their foraging success by shoaling with native Mexican species, and potentially increase the chances of invasion success. However, do native individuals tend to associate with invaders as well? We tested the hypothesis that the twoline skiffia (Neotoca bilineata) and the Lerma livebearer (Poeciliopsis infans), both native endemic Mexican topminnows, will associate with guppies, a notorious invasive species present in Mexico. Our investigation shows that guppies, twoline skiffias and Lerma livebearers have a mutual tendency to associate with each other. Although there is a marked tendency to shoal with heterospecifics in this system, shoaling partners do not necessarily benefit equally from the association. Further research on invasive-native social interactions is needed to promote our understanding of potential facilitation by natives.