Alfredo F. Ojanguren

Uncoupling the links between male mating tactics and female attractiveness

Because not all females are equally attractive, and because mating reduces the chances of getting further copulations, males should prefer better-quality mates. In this paper, we use the Trinidadian guppy (Poecilia reticulata) to explore the effects of two non–correlated measures of female quality—size and reproductive status—on male mating decisions. All male guppies employ two alternative mating tactics. We found that large females, particularly those from a high predation site, were the target of most sneaky mating attempts. The response persisted in fish raised under standard conditions over several generations in the laboratory. In addition, non-pregnant females received more courtship displays. We conclude that males can discriminate among females and that they uncouple their mating tactics to track different axes of quality.

Male harassment reduces short-term female fitness in guppies

[Males can maximise their fitness by copulating with as many females as possible. Although this behaviour may have negative consequences for the females involved, females can also benefit from multiple mating. For example, multiple mated female guppies produce more, larger and fitter offspring. It is not clear if these fitness benefits are a direct result of multiple mating, or the product of female choice — either pre or post copulatory — for better quality males. To answer this question, individual virgin female guppies were exposed to different combinations of males: just one male; three males, one at a time; and three males presented simultaneously. Mating activity was more intense in the three-at-a-time treatment but did not differ between the other two. This increased attention did not affect gestation time nor offspring size, but significantly reduced the number of offspring produced. This reveals that male harassment causes a direct reduction in female short-term fitness., Males can maximise their fitness by copulating with as many females as possible. Although this behaviour may have negative consequences for the females involved, females can also benefit from multiple mating. For example, multiple mated female guppies produce more, larger and fitter offspring. It is not clear if these fitness benefits are a direct result of multiple mating, or the product of female choice — either pre or post copulatory — for better quality males. To answer this question, individual virgin female guppies were exposed to different combinations of males: just one male; three males, one at a time; and three males presented simultaneously. Mating activity was more intense in the three-at-a-time treatment but did not differ between the other two. This increased attention did not affect gestation time nor offspring size, but significantly reduced the number of offspring produced. This reveals that male harassment causes a direct reduction in female short-term fitness.]

Association tendency and preference for heterospecifics in an invasive species.

Animals gain benefits by forming groups with phenotypically and behaviourally similar individuals. The most common groups are homogenous, composed by conspecifics, although in some cases associations of similar organisms of different species have been reported when individuals benefit from it. In this study, we tested the prediction that the Trinidadian guppy, Poecilia reticulata, a fish that has successfully invaded at least 70 countries, will shoal with heterospecifics. We measured shoaling tendency and shoal companion preference in wild-caught female guppies when they encounter two heterospecific species: the native Poecilia picta and the non-native Poecilia sphenops, a poeciliid recently introduced in Trinidad. Our results show that guppies have a higher tendency to shoal with conspecifics; if the alternative is be alone, they readily shoal with both species even when they have had no previous experience with other poeciliids. Individuals in these associations could benefit from safety in numbers along with other advantages of group living. This predisposition to associate with other species that share similar ecological conditions could explain the guppy’s success as invasive species as it enables them to increase their shoal size during the first stages of invasion and thus avoid Allee effects.

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

Sociability in animals provides benefits such as reduced predation risk and increased foraging efficiency. During the early stages of invasion, individuals are often vulnerable as part of a small population (Allee effects); associations with native heterospecifics could mitigate some of the disadvantages of small population size and thereby increase the chances of establishment success. Here we explored two potential benefits of heterospecific association to guppies, Poecilia reticulata, a very successful invasive species. We first investigated whether guppies can exploit visual cues from morphologically similar heterospecific individuals as effectively as those from conspecifics. We next tested whether willingness to explore an unfamiliar environment depends on whether guppies are accompanied by conspecifics or heterospecifics. Our results show that guppies can acquire information on food availability from another species, as well as from conspecifics. We also found that guppies engaged in exploratory behaviour more quickly if the habitat had plants in it, and were more likely to associate if it was unstructured; there was, however, no difference in the frequency with which the focal fish was accompanied by a conspecific or a heterospecific individual. These results show that guppies respond to these heterospecifics as they do with conspecifics. Our study reveals some of the traits that could make an invader successful and potentially help to identify species with a higher potential to become established outside their native range.

Sexual segregation in monomorphic minnows

Sexual segregation, where males and females use habitat in different ways, is widespread among animals including fish, and has important consequences for key aspects of population ecology including foraging success, predator avoidance and growth. However, currently, evidence for sexual segregation is based on observations of sexually dimorphic species or species with differing reproductive strategies. We used European minnows, Phoxinus phoxinus, to test the null hypothesis that sexual segregation does not occur in sexually monomorphic species. A large, seminatural stream channel equipped with passive integrated transponder (PIT) detectors monitored the activity of 70 fish for 98 days on ecologically relevant spatial and temporal scales. Sexual segregation was evident spatially (with males and females using different habitats within the stream), temporally (males switched patches more frequently than females at night, but not during the day) and socially (with males, but not females, demonstrating same-sex association preferences). Our results are the first to demonstrate sexual segregation in monomorphic species outside the breeding season. We discuss potential explanations for our observations and ways in which patterns of variation in activity, space use and social interactions have important implications for population dynamics.

Exotic invaders gain foraging benefits by shoaling with native fish

Freshwater habitats are under increasing threat due to invasions of exotic fish. These invasions typically begin with the introduction of small numbers of individuals unfamiliar with the new habitat. One way in which the invaders might overcome this disadvantage is by associating with native taxa occupying a similar ecological niche. Here we used guppies (Poecilia reticulata) from a feral population in Mexico to test the prediction that exotic shoaling fish can associate with heterospecifics, and that they improve their foraging efficiency by doing so. Guppies have invaded the Mexican High Plateau and are implicated in the declines of many native topminnow (Goodeinae) species. We show that heterospecific associations between guppies and topminnows can deliver the same foraging benefits as conspecific shoals, and that variation in foraging gains is linked to differences in association tendency. These results uncover a mechanism enabling founding individuals to survive during the most vulnerable phase of an invasion and help explain why guppies have established viable populations in many parts of Mexico as well in every continent except Antarctica.

Interspecific synchrony of seabird population growth rate and breeding success

Environmental variability can destabilize communities by causing correlated interspecific fluctuations that weaken the portfolio effect, yet evidence of such a mechanism is rare in natural systems. Here, we ask whether the population dynamics of similar sympatric species of a seabird breeding community are synchronized, and if these species have similar exceptional responses to environmental variation. We used a 24-year time series of the breeding success and population growth rate of a marine top predator species group to assess the degree of synchrony between species demography. We then developed a novel method to examine the species group – all species combined – response to environmental variability, in particular, whether multiple species experience similar, pronounced fluctuations in their demography. Multiple species were positively correlated in breeding success and growth rate. Evidence of “exceptional” years was found, where the species group experienced pronounced fluctuations in their demography. The synchronous response of the species group was negatively correlated with winter sea surface temperature of the preceding year for both growth rate and breeding success. We present evidence for synchronous, exceptional responses of a species group that are driven by environmental variation. Such species covariation destabilizes communities by reducing the portfolio effect, and such exceptional responses may increase the risk of a state change in this community. Our understanding of the future responses to environmental change requires an increased focus on the short-term fluctuations in demography that are driven by extreme environmental variability.

How pre- and postcopulatory sexual selection influence male mating decisions in a promiscuous species

When females mate multiply, male reproductive success depends on both pre- and postcopulatory processes, including female choice and sperm competition. However, these processes can favour different mating tactics in males. Here we used the Trinidadian guppy, Poecilia reticulata, system to understand how this conflict is resolved. We asked whether knowledge of recent female mating history leads males to adjust their mating effort with respect to the time devoted to mating activity, and the frequency and the sequence of mating tactics employed. To do this we quantified male mating behaviour in three competitive scenarios: (1) Single, when a focal male arrives near a single female and remains alone with her; (2) First, when a focal male is joined by a rival male; and (3) Second, when a focal male arrives after a rival male. We hypothesized that males adjust their behaviour based on arrival order. If female sequential mate choice is the main process shaping male mating behaviours (favouring First males in guppies), males should avoid competition and invest most when Single. Alternatively, if last-male sperm precedence is the major driver of decision making, males should invest more in mating attempts in the Second scenario. Greatest investment when First implies an intermediate strategy. We found that order of arrival influenced mating decisions with most mating activity during the First rather than the Single and Second scenarios. This result suggests that both pre- and postcopulatory processes influence mating investment, and that individual males make contingent decisions to maximize both mating and fertilization success.

The effect of water temperature on routine swimming behaviour of new born guppies (Poecilia reticulata).

Guppies have successfully established populations in places with thermal regimes very different from the Tropical conditions in their native range. This indicates a remarkable capacity for thermal adaptation. Given their vulnerability to predation as juveniles, acute changes in temperature, which can alter predator-prey relationships, can impact juvenile survival and have amplified consequences at the population level. To understand how temperature may impact juvenile survival and gain insight into their success as an invasive species, we researched the effect of acute temperature changes on the routine swimming behaviour of juvenile guppies. Using a novel 3-dimensional tracking technique, we calculated 4 routine swimming parameters, speed, depth, and variation in speed or depth, at 6 different test temperatures (17, 20, 23, 26, 29, or 32°C). These temperatures cover their natural thermal range and also extended past it in order to include upper and lower thermal limits. Using model selection, we found that body length and temperature had a significant positive relationship with speed. Variation in speed decreased with rising temperatures and fish swam slightly closer to the bottom at higher temperatures. All juveniles increased variation in depth at higher temperatures, though larger individuals maintained slightly more consistent depths. Our results indicate that guppies have a large thermal range and show substantial plasticity in routine swimming behaviours, which may account for their success as an invasive species.

Comment on “International Conservation Policy Delivers Benefits for Birds in Europe”

Donald et al. (Reports, 10 August 2007, p. 810) assessed the impact of the European Unions Birds Directive, a conservation policy enacted in 1979, and reported evidence for positive population changes in targeted species. We argue that their conclusions are overstatements based on unsuitable data and inappropriate analyses.