Boxer crabs induce asexual reproduction of their associated sea anemones by splitting and intraspecific theft.

Crabs of the genus Lybia have the remarkable habit of holding a sea anemone in each of their claws. This partnership appears to be obligate, at least on the part of the crab. The present study focuses on Lybia leptochelis from the Red Sea holding anemones of the genus Alicia (family Aliciidae). These anemones have not been found free living, only in association with L. leptochelis. In an attempt to understand how the crabs acquire them, we conducted a series of behavioral experiments and molecular analyses. Laboratory observations showed that the removal of one anemone from a crab induces a "splitting" behavior, whereby the crab tears the remaining anemone into two similar parts, resulting in a complete anemone in each claw after regeneration. Furthermore, when two crabs, one holding anemones and one lacking them, are confronted, the crabs fight, almost always leading to the "theft" of a complete anemone or anemone fragment by the crab without them. Following this, crabs "split" their lone anemone into two. Individuals of Alicia sp. removed from freshly collected L. leptochelis were used for DNA analysis. By employing AFLP (Fluorescence Amplified Fragments Length Polymorphism) it was shown that each pair of anemones from a given crab is genetically identical. Furthermore, there is genetic identity between most pairs of anemone held by different crabs, with the others showing slight genetic differences. This is a unique case in which one animal induces asexual reproduction of another, consequently also affecting its genetic diversity.

Generalization and discrimination of positive and negative acoustic stimuli in the common carp (Cyprinus carpio).

Groups of common carp (Cyprinus carpio) were trained for 33 days to discriminate between two acoustic signals differing in frequency and temporal pattern. One signal (positive stimulus) was reinforced by food, while the other (negative stimulus) was not rewarded. When exposed to 3 positive and 3 negative stimuli per day (training Paradigm 1) the fish responded similarly to the two signals. When daily negative stimuli outnumbered positive stimuli (3 positive and 33 negative, training Paradigm 2) the fish responded similarly to the two signals for the first 2 weeks and then began to discriminate between them. Discriminatory response was statistically significant from Day 21 of training. After 33 days, training was switched from Paradigm 2 to Paradigm 1 and the fish maintained their discriminatory capability. The results are interpreted in terms of anticipatory frustration and risk management.

Intersexuality and behavior in crayfish: the de-masculinization effects of androgenic gland ablation.

In crustaceans, male differentiation and primary and secondary characteristics are regulated by the androgenic gland (AG). In gonochoristic crustaceans, the AG is also linked to intersexuality. Whereas the co-occurrence of various male and female characteristics has been demonstrated in intersex crustaceans, little is known regarding sexually dimorphic behavior patterns in such individuals. In the present study, we used an intersex crayfish model to investigate--for the first time in crustaceans--the agonistic and mating behavior of intersex individuals, and to explore the effects of AG ablation on behavior, morphology and physiology. As was the case for their morphological and physiological reproductive traits, intersex individuals--despite being genotypically females--generally resembled males in terms of behavior: they engaged in fighting with males and copulated with receptive females. However, fighting durations of intersex animals were intermediate between those of males and females, and the durations of the copulations were remarkably short. Adult intersex individuals that had been AG ablated at the juvenile stage were unlikely to engage in fighting with males (similar behavior to females) and did not exhibit any mating behavior with receptive females. AG ablation resulted in feminine morphological and physiological shifts in the treated intersex individuals and enabled vitellogenin gene transcription and the onset of secondary vitellogenesis. It thus appears that an as-yet-unknown AG-secreted factor(s) regulating maleness also seems to regulate the organization of male behavior in crustaceans.

Inducible reproductive plasticity of the guppy Poecilia reticulata in response to predation cues.

Predation has long been described as one of the major driving forces in evolution. Guppies (Poecilia reticulata) from natural populations exposed to different predation pressures, were found to have different life history traits. Reproductive plasticity in response to direct predation cues has mainly been reported for invertebrates. The goals of the present study were to determine whether exposure to predation cues would induce reproductive phenotypic plasticity in female guppies and to determine whether the effective cues are visual, chemical, or a combination of both. In our first experiment, female guppies exposed to predation cues of the african cichlids Aulonocara nyassae increased their reproductive output by almost two fold, having larger brood-sizes and shorter brood-interval at the first spawn. This effect disappeared in the second spawn in the absence of predators. In the second experiment we found that exposure to the predators induced an increase in the brood-size regardless of whether the cue was: only visual, only chemical, visual and chemical or visual, chemical and tactile. The impacts of these cues were equally powerful on the tested variables and they did not have any cumulative effect. Similar to the results of the first experiment, this effect disappeared in the second spawn, in the absence of predation cues. The present study demonstrates a direct immediate and reversible effect of predation cues on guppy reproduction.

Male-like behavioral patterns and physiological alterations induced by androgenic gland implantation in female crayfish.

The androgenic gland (AG) has been shown to regulate male sexual differentiation and secondary male characteristics in Crustacea. This study presents for the first time in crustaceans evidence for masculinization effects of the AG on reproductive behavior, in addition to morpho-anatomical and physiological effects. AG implantation into immature female red claw crayfish Cherax quadricarinatus inhibited secondary vitellogenesis and development of the ovaries, as well as morphological traits that facilitate maternal egg brooding; it also caused the appearance of secondary male characteristics. However, primary male characteristics and a masculine reproductive system were not developed. In pair encounters, aggression was substantially lower in interactions between AG-implanted and intact females than in interactions within AG-implanted or intact pairs. Moreover, elements of mating behavior, i.e. male courtship displays and false copulations, were exhibited by AG-implanted females in several encounters with intact females. In addition to known morpho-anatomical and physiological effects of the AG in crustaceans, the present study suggests that the AG has novel effects on the neural network that generates social behavior.