Are some individuals generally more behaviorally plastic than others? An experiment with sailfin mollies

Abstract

Individuals within the same population generally differ among each other not only in their behavioral traits but also in their level of behavioral plasticity (i.e., in their propensity to modify their behavior in response to changing conditions). If the proximate factors underlying individual differences in behavioral plasticity were the same for any measure of plasticity, as commonly assumed, one would expect plasticity to be repeatable across behaviors and contexts. However, this assumption remains largely untested. Here, we conducted an experiment with sailfin mollies (Poecilia latipinna) whose behavioral plasticity was estimated both as the change in their personality traits or mating behavior across a social gradient and using their performance on a reversal-learning task. We found that the correlations between pairwise measures of plasticity were weak and non-significant, thus indicating that the most plastic individuals were not the same in all the tests. This finding might arise because either individuals adjust the magnitude of their behavioral responses depending on the benefits of plasticity, and/or individuals expressing high behavioral plasticity in one context are limited by neural and/or physiological constraints in the amount of plasticity they can express in other contexts. Because the repeatability of behavioral plasticity may have important evolutionary consequences, additional studies are needed to assess the importance of trade-offs between conflicting selection pressures on the maintenance of intra-individual variation in behavioral plasticity.

Keywords: Behavioral plasticity; General plasticity; Individual differences; Sailfin mollies.

Figure 1. Top view of the tank used to measure exploration and anxiety.

The four containers, placed in each corner of the tank, housed a single individual when the fish was tested with an audience or were kept empty otherwise. The gray area delimits the area considered to measure anxiety in the alone treatment.

Figure 2. Top view of the tank used to measure neophobia.

The tank was divided into three identical sections (30 × 20 cm) by two opaque removable partitions (blue dotted lines). Section 1 contained a transparent box used to confine the audience males, Section 2 was equipped with two plastic plants that could be used as a shelter, and Section 3 contained a novel object and a food box.

Figure 3. Top view of the tank used to measure reversal learning speed.

The tank was divided in two sections (30 × 30 cm) by a transparent removable partition (blue dotted line): an observation compartment and a choice compartment divided into two corridors. Two visual cues (a blue square and a yellow cross of around 4 × 4 cm) were placed both in front and at the end of each corridor to ensure that the fish could see them from the observation compartment and learn which cue was rewarded.

Figure 4. Mean (±SEM) behavioral plasticity in neophobia (A) and exploration (B) measured under three different social gradients.

Behavioral plasticity was estimated as the difference in absolute value between (i) the two replicates of the alone treatment (gradient A), (ii) the two replicates of the audience treatment (gradient B), and (iii) the mean trait value in the alone treatment and the mean trait value in the audience treatment (gradient C).