Micaria sociabilis exhibited a repeatable behavioural trait, suggesting it is a stable component of male personality. However, aggressiveness was not associated with either copulation or the likelihood of reversed cannibalism, implying other factors are at play. Interestingly, the frequency of reversed cannibalism varied significantly between spring and summer generations, although no seasonal variation was found for copulation frequency. While male aggressiveness did not correlate with attack behaviour toward females, seasonality had a notable effect, with males being more likely to attack in summer compared to spring. Below, we discuss each of these findings and propose potential explanations for the observed patterns.
The repeatability of male aggressiveness, as indicated by the number of overkilled prey, was found to be high, suggesting that this trait is consistent across time and different contexts for individual males. High repeatability in behavioural traits is often indicative of a stable personality component (Réale et al. 2007). This finding supports the notion that aggression may be an intrinsic, stable trait in M. sociabilis males, potentially serving as an adaptive strategy in prey acquisition or mating situations.
Contrary to our expectations, male aggressiveness had no significant effect on the likelihood of reversed cannibalism. This is surprising because aggressive behaviours often correlate with boldness and risk-taking traits (Sih et al. 2004) that could influence the outcome of male-female interactions in cannibalistic species. The lack of association may suggest that reversed cannibalism could be a more opportunistic behaviour, less tied to consistent personality traits, and more affected by immediate physiological conditions (i.e., hunger, nutrient deficiency, or other stress). Alternatively, reversed cannibalism in M. sociabilis might be driven by other factors unrelated to male aggression, such as female condition (body quality, age), as indicated by Sentenská and Pekár (2013). Alongside female age, we assume that further patterns such as the mating status of both sexes may also shape the occurrence of reversed cannibalism.
We also expected that aggressiveness might correlate with male body size, and that the bigger the male, the more cannibalistic it is (Sentenská and Pekár 2013). Our study failed to confirm this. We speculate that body size might not have a simple linear relationship with aggression or cannibalism. It is also hard to conclude that there is an optimal size range for males where reversed cannibalism occurs most frequently. Furthermore, some studies have also reported no correlation between body size and aggression (Bakker 1986; FitzGerald and Kedney 1987). It is also possible that aggression might be driven more by individual personality traits or behavioural syndromes than by physical size. This means that smaller males could be just as aggressive as larger males, leading to no observable size-based pattern in aggression or cannibalism. In another block of experiments, we observed that small males frequently and successfully attacked females almost twice their size, such attacks sometimes resulting in cannibalism (unpublished data).
We concur with Sentenská and Pekár (2013) that deciding whether males were attempting to copulate or kill the female was challenging, as both behaviours share similar patterns, such as active pursuit by the male and brief front-leg attacks. As a result, in our records where neither copulation nor cannibalism occurred within the allotted time (20 minutes), potential data on these behaviours may have been missed, leading to gaps in our understanding of the outcomes. Further examination of male behaviour is essential to better understand the motivations behind copulation attempts versus lethal attacks on females also in natural circumstances.
Another intriguing question is when the male’s decision to cannibalize or mate is made. In our experiments, we observed several males abruptly kill a female upon contacting her, while in other cases males performed short attacks following an encounter with a female. This suggests that the decision by males is made before contact with a female. In Philodromus cespitum Wlackenaer, males were able to recognize fine-scale information about the female’s mating status (i.e., virginity and the presence of a plug) from her dragline silk (Sentenská and Pekár 2019). We witnessed males following the dragline; thus, their decision to cannibalize could be made on the basis of information from the dragline.
It is worth mentioning that males also differed in their motivations to kill females. Some males only killed females but did not consume them, which indicates that nutritional motivation can be excluded. The most often-proposed assumption is that sexual cannibalism happens to prevent starvation (Elgar 1992). Indeed, several studies have confirmed that hungry individuals tend to kill their partners at a higher rate than satiated ones (e.g., Andrade 1996, 1998; Schneider and Elgar 2001; Wilder and Rypstra 2008; Roggenbuck et al. 2011). However, the previous study by Sentenská and Pekár (2014) on M. sociabilis similarly found no significant difference between well-fed and food-deprived males in laboratory experiments, consistent with our results.
We failed to find that male aggressiveness affects the copulation frequency either, although previous studies in other species reported that aggressiveness and/or boldness correlate with reproductive success (Sih et al. 2004; reviewed by Schuett et al. 2010; Munson et al. 2020). We suspect the impact of male aggressiveness might be species-specific and/or dependent on the context in which it is displayed. For example, aggressiveness in this species could be more important in male-male competition or resource acquisition than in interactions with females. If aggressiveness primarily serves to deter rival males, it may not play a direct/primary role in influencing copulation success with females. It appears that copulation frequency is more influenced by female status, particularly mating experience (e.g., plug presence), and possibly age. Our data suggest that high copulation occurred with females in the spring period and with virgin females. Surprisingly, the last finding contradicts what was revealed by Sentenská and Pekár (2013); however, it fits the general pattern of male preference for virgin females, widespread among entelegyne spiders (e.g., Austad 1982; Herberstein et al. 2002; Gaskett et al. 2004; Stoltz et al. 2007, but see Elgar 1998; Eberhard 2004). Moreover, in the cannibalistic wolf spider Allocosa brasiliensis (Petrunkevitch), males also preferentially copulate with virgin females, while mostly killing those which have already mated (Aisenberg et al. 2011).
Furthermore, we found that the female plug size was not predicted by male aggressiveness, male body size, or season. In our study, we lacked accurate information about the mating statuses of females used in the mating experiments. It is often possible that females with no plug can also be non-virgin, as not all males may apply plugs during mating. However, it is interesting to mention here that the plug was present in all ignored or cannibalized non-virgin females (they were checked only after the mating trial was completed see Mating trial experiment). This indicates the high probability of those females already being plugged before, i.e. having a mated status, according to which we may conclude that plug presence can act as one of the indicators for subsequent male behaviour, which has also been documented in other spider species (Schneider and Lesmono 2009). A previous study also reported that M. sociabilis males are not highly successful in removing the plug and/or show little interest in mating with plugged females (Sentenská et al. 2015).
The seasonal effect on reversed cannibalism was significant, with males being more likely to cannibalize females in July compared to April. It is reasonable to assume that seasonal variation may be linked to a factor such as the natural history, maturation rate, or physiological condition of the species (female receptivity or hormonal levels) or to differences in environmental conditions, such as temperature, humidity, photoperiod changes, or food availability, which could, on the whole, influence mating scenarios or reproductive patterns. For instance, April might indicate the beginning of the breeding season when females are sexually more receptive, and males are more motivated to mate (before the peak of competition later in the season) rather than cannibalize them. Our observation of females behaving in a more selective way toward males in spring compared to summer might support this statement. In contrast, the frequency of copulation was not affected by the season, with no significant difference between April and July. This suggests that copulation may not be strongly influenced by temporal or broader seasonal trends such as the breeding season or environmental conditions. Given the multitude of interacting factors, further research, including controlled experiments (e.g., using energetically stressed males and well-fed males) and detailed ecological observations, would be necessary to clarify whether cannibalism is an adaptive strategy based on immediate need rather than personality, or to unravel the specific mechanisms driving these seasonal variations in M. sociabilis behaviour.