Plasticity in extended phenotype increases offspring defence despite individual variation in web structure and behaviour

Abstract

Many animals actively defend their offspring using a range of behaviours from calling and mobbing in birds, to physical grappling in crustaceans, and the expression of these behaviours positively scale with offspring value. While this role of behaviour in defence is well studied, very little is known about how other traits, specifically the structure of architectural constructions such as webs and nests, contribute to offspring defence. Additionally, although some tax a show consistent individual differences in offspring defence behaviour, it is completely unknown whether individuals also differ in defensive structures. We addressed these questions in the redback spider, Latrodectus hasselti, by measuring how a female laying an eggcase influences female behaviour and web structure, and whether those traits scale with relative reproductive investment. Our results show that females modified web structure in response to an eggcase, but only the protective elements of web structure positively scaled with the relative value of that eggcase. Finally, despite the significant correlations, fixed effects (e.g. eggcase possession/value) in the models explained only 5–23% of the variation in behaviour and web structure, while the random effect of individual identity explained 46–65% of the variation. This variation drove moderate to high repeatability estimates across all traits, suggesting that some individuals consistently invest relatively more in defence, while some invest less. These results highlight that extended phenotypic traits may be a critical component of offspring defence in some taxa. Furthermore, individual variation in these traits suggest that different reproductive strategies may exist, whereby some individuals invest more in reproduction at a cost to safety/foraging and vice versa.

Repeatability but no short‐term plasticity in the web architecture ofLatrodectus hesperuswestern black widow spiders (Araneae: Theridiidae)

“…We conclude that plasticity in an extended phenotype can be context dependent. Although we detected no plasticity in black widow web architecture in response to their experience of the site of prey capture, other studies have found these spiders to modify their webs in response to other factors (short‐term physiological or environmental changes) (Blackledge & Zevenbergen, ; DiRienzo & Aonuma, ; Zevenbergen et al, ). Further, orb‐web spiders do vary web architecture according to their experience of the site of prey capture (Heiling & Herberstein, ; Nakata, ).…”

“…Alternatively, web plasticity in these spiders may follow cues other than experience of the site of prey capture. For example, the spiders might respond to differences in prey features; for example, the type of vibrations they make on the web or their behavior as they struggle to break free (Escalante, ) (and see also DiRienzo & Aonuma, ; Zevenbergen et al, ). Another possibility is that the spiders may vary web architecture when prey are less plentiful, or that they vary an aspect of web design that we did not measure (e.g., the planar extent of the sheet, which was fixed in our experiment by the size of the frames we gave them).…”

“…Extended phenotypes—constructions like termite cities, caddisfly houses, and beaver dams—are often the product of animal behavior (Dawkins, ). Consequently, the adjustability of behavior (Zuk, Bastiaans, Langkilde, & Swanger, ) may allow animals to make extended phenotypes adaptively plastic, according to the conditions in which they are built (Blamires, ; Blamires, Martens, & Kasumovic, ; Craig, ; DiRienzo & Aonuma, ; Head, Fox, & Barber, ). However, extended phenotypes are also relatively stable and long‐lasting, in comparison with the behavior that produced them (Schaedelin & Taborsky, ).…”

Male and female preferences for nest characteristics under paternal care

“…We cannot distinguish whether this extra nest-building effort occurred prior to female spawning, then leaving the option that females were also attracted to building behavior as a potentially honest male quality signal (Zahavi, 1975), or after spawning, when nest amendments were linked to another trait like displacement fanning (Olsson et al, 2009;Svensson & Kvarnemo, 2005). Preferred males would thus invest more in nest building as part of their brood care similar to observations in birds and spiders (DiRienzo & Aonuma, 2018;Soler, Cuervo, Møller, & DeLope, 1998).…”

Orb-weaving spiders show a correlated syndrome of morphology and web structure in the wild

“…It also allows us to see if there is day-to-day variation in web structure, if for example certain environmental conditions consistently influence web structure for all individuals. Previous studies on among-individual consistency in web structure have been conducted in captivity (Dirienzo and Montiglio 2016; Montiglio and DiRienzo 2016; Dirienzo and Montiglio 2016 Jul; DiRienzo and Dornhaus 2017; DiRienzo and Aonuma 2018), but our study took place in the wild to assess the degree of consistency of behaviour and web structure, and how they covary with each other and with spider body size, in a natural setting. Studies in standardised laboratory settings are useful when we want to control for external factors, but studies in free-living populations help us assess the degree of consistency and correlations between traits that natural selection may be acting upon.…”