Odour cues from suitors' nests determine mating success in a fish

Mate Discrimination Using Chemical Cues by Male Guppies

Males often perform mate choice with the aim of maximizing reproductive success. To identify profitable mates, the males of some animals are known to use visual and chemical cues derived from females. In this study, we aimed to examine mate discrimination by male guppies (Poecilia reticulata) using chemical cues received from females under different reproductive statuses, i.e., virgin females, pregnant females, females after copulation with another male, and post-partum females. We conducted a dichotomous choice experiment for each combination of chemical stimuli from females under different reproductive statuses. In experiment 1, in which females were removed from water that was subsequently used as a chemical stimulus, male preferences did not differ significantly in all combinations of chemical stimuli from females under different reproductive statuses. However, in experiment 2, in which females remained within bottles containing the water used as a chemical stimulus, with the exception of one combination of chemical stimuli, significant differences in male preferences were detected for chemical stimuli derived from females under different reproductive statuses. Overall, males generally showed a preference for chemical stimulus received from females after copulation with other males. The findings of this study indicate that male guppies can discriminate the reproductive status of females based solely on chemical cues that may disappear or degenerate within a short period of time, thereby facilitating profitable mate choice.

Burying Beetle Parents Adaptively Manipulate Information Broadcast from a Microbial Community

AbstractMicrobial volatiles provide essential information for animals, which compete to detect, respond to, and perhaps control this information. Burying beetle parents have the opportunity to influence microbially derived semiochemicals, because they monopolize a small carcass for their family, repairing feeding holes and applying exudates that alter the microbial community. To study adaptive manipulation of microbial cues, we integrated mechanistic and functional approaches. We contrasted gas chromatography-mass spectrometry (GC-MS) volatile profiles from carcasses that were or were not prepared by a resident pair of Nicrophorus orbicollis. Methyl thiocyanate (MeSCN), the primary attractant for burying beetles seeking a fresh carcass, was reduced 20-fold by carcass preparation, while dimethyl trisulfide (DMTS), which deters breeding beetles, was increased 20-fold. These results suggest that parental care serves to make previously public information more private (crypsis, MeSCN) and to disinform rivals with a deterrent (DMTS). Functional tests in the field demonstrated that carcass preparation reduced discovery and use by congeners (threefold) as well as by dipteran rivals. Because microbes and their chemicals influence nearly every aspect of animal ecology, animal manipulation of microbial cues may be as widespread as manipulation of their own signals.

Post-glacial establishment of locally adapted fish populations over a steep salinity gradient

Studies of colonization of new habitats that appear from rapidly changing environments are interesting and highly relevant to our understanding of divergence and speciation. Here, we analyse phenotypic and genetic variation involved in the successful establishment of a marine fish (sand goby, Pomatoschistus minutus) over a steep salinity drop from 35 PSU in the North Sea (NE Atlantic) to two PSU in the inner parts of the post-glacial Baltic Sea. We first show that populations are adapted to local salinity in a key reproductive trait, the proportion of motile sperm. Thereafter, we show that genome variation at 22,190 single nucleotide polymorphisms (SNPs) shows strong differentiation among populations along the gradient. Sequences containing outlier SNPs and transcriptome sequences, mapped to a draft genome, reveal associations with genes with relevant functions for adaptation in this environment but without overall evidence of functional enrichment. The many contigs involved suggest polygenic differentiation. We trace the origin of this differentiation using demographic modelling and find the most likely scenario is that at least part of the genetic differentiation is older than the Baltic Sea and is a result of isolation of two lineages prior to the current contact over the North Sea-Baltic Sea transition zone.

The endocrine disruptor, 17α-ethinyl estradiol, alters male mate choice in a freshwater fish

Among the handful of studies on the behavioural effects of endocrine disrupting chemicals (EDCs), only a few have set out to disentangle the mechanisms underpinning behavioural changes. In fish, previous studies have shown that both visual and chemical cues play an important role in mate choice. As such, contaminant-induced changes in either transmission or perception of mate choice cues could have direct implications for individual's fitness. One widespread contaminant of environmental concern is 17α-ethinyl estradiol (EE2), a synthetic estrogen used in the contraceptive pill. Here, we investigated the impacts of EE2 exposure (28 days; measured concentration 14 ng/L) on visual and chemical communication in wild guppies (Poecilia reticulata). Using a standard dichotomous mate choice assay, we first gave individual males (either control or EE2-exposed) the opportunity to court two size-matched females (one control and one EE2-exposed) using only visual cues. We then introduced chemical cues of females (control and EE2-exposed) to the trial tank. We found that there was no significant effect of EE2-treatment on total time males spent associating with the females, when given only visual cues. There was, however, a significant effect on male courtship behaviour, with both control and EE2-exposed males spending more time performing 'sigmoid' displays towards the visual cues of control females compared to EE2-exposed females. When males were presented with both visual and chemical female cues simultaneously, we found that males spent more time courting control females that were paired with EE2-chemical cues. Not only does our study uncover a previously unknown behavioural impact of EE2-exposure on chemical cues, but demonstrates that EE2-exposure can exert complex effects on visual and chemical communication in a mate choice context. Finally, we contribute to the discussion of intraspecific variability by providing data on the potential trade-offs underpinning contaminant-induced behavioural changes.

Smell of Infection: A Novel, Noninvasive Method for Detection of Fish Excretory-Secretory Proteins

Chemical signals are produced by aquatic organisms following predatory attacks or perturbations such as parasitic infection. Ectoparasites feeding on fish hosts are likely to cause release of similar alarm cues into the environment due to the stress, wounding, and immune response stimulated upon infection. Alarm cues are often released in the form of proteins, antimicrobial peptides, and immunoglobulins that provide important insights into bodily function and infection status. Here we outline a noninvasive method to identify potential chemical cues associated with infection in fish by extracting, purifying, and characterizing proteins from water samples from cultured fish. Gel free proteomic methods were deemed the most suitable for protein detection in saline water samples. It was confirmed that teleost proteins can be characterized from water and that variation in protein profiles could be detected between infected and uninfected individuals and fish and parasite only water samples. Our novel assay provides a noninvasive method for assessing the health condition of both wild and farmed aquatic organisms. Similar to environmental DNA monitoring methods, these proteomic techniques could provide an important tool in applied ecology and aquatic biology.

Do male sticklebacks use visual and/or olfactory cues to assess a potential mate's history with predation risk?

Differential allocation occurs when individuals alter their reproductive investment based on their mate's traits. A previous study showed that male threespine sticklebacks, Gasterosteus aculeatus, reduced courtship towards females that had previously been exposed to predation risk compared to unexposed females. This suggests that males can detect a female's previous history with predation risk, but the mechanisms by which males assess a female's history are unknown. To determine whether males use chemical and/or visual cues to detect a female's previous history with predation risk, we compared rates of courtship behaviour in the presence of visual and/or olfactory cues of predator-exposed females versus unexposed females in a 2×2 factorial design. We found that males differentiate between unexposed and predator-exposed females using visual cues: regardless of the olfactory cues present, males performed fewer zigzags (a conspicuous courtship behaviour) when they were exposed to visual cues from predator-exposed females compared to unexposed females. However, males' response to olfactory cues changed over the course of the experiment: initially, males performed fewer courtship displays when they received olfactory cues of predator-exposed females compared to unexposed females, but they did not discriminate between cues from predator-exposed and unexposed females later in the experiment. A follow-up experiment found that levels of cortisol released by both predator-exposed and unexposed females decreased over the course of the experiment. If cortisol is linked to or correlated with olfactory cues of predation risk that are released by females, then this suggests that the olfactory cues became less potent over the course of the experiment. Altogether, these results suggest that males use both visual and olfactory cues to differentiate between unexposed and predator-exposed females, which may help ensure reliable communication in a noisy environment.

Water mold infection but not paternity induces selective filial cannibalism in a goby

Many animals heavily invest in parental care but still reject at least some of their offspring. Although seemingly paradoxical, selection can favor parents to neglect offspring of particularly low reproductive value, for example, because of small survival chances. We here assess whether filial cannibalism (FC), where parents routinely eat some of their own young, is selective in response to individual offspring reproductive value. We performed two independent laboratory experiments in the common goby (Pomatoschistus microps) to test whether caring fathers preferentially cannibalize eggs of a given infection history and paternity. While males did not discriminate kin from nonkin eggs, they consumed significantly more eggs previously exposed to water mold compared to uninfected eggs. Our findings clearly show that parents differentiate between eggs based on differences in egg condition, and thus complement the prevailing view that FC arises for energetic reasons. By preventing the spread of microbial infections, the removal of molded eggs can constitute an important component of parental care and may represent a key driver of selective FC in a wide array of parental fish.