Individual Morphology and Habitat Structure Alter Social Interactions in a Range-Shifting Species

Abstract

Ecosystem engineers that serve as foundation species shape the ecology and behavior of the species which depend on them. As species shift their geographic ranges into ecosystems they have not previously inhabited, it is important to understand how interactions with novel foundation species alter their behavior. By employing behavioral assays and morphological analyses, we examined how individual morphology and foundation species structure impact the ritualistic aggression behavior of the range shifting mangrove tree crab Aratus pisonii between its historic and colonized habitats. Structure of the foundation species of the colonized salt marsh ecosystem increases the incidence and risk of this behavior over the historic mangrove habitat, potentially negating benefits of ritualizing aggression. Further, docks within the salt marsh, which are structurally analogous to mangroves, mitigate some, but not all, of the increased costs of performing ritualized aggression. Crabs in the salt marsh also had relatively larger claws than conspecifics from the dock and mangrove habitats, which has implications for the risk and outcomes of ritualized interactions. These changes to morphology and behavior highlight the impacts that foundation species structure can have on the morphology, ecology, and behavior of organisms and the importance of studying these impacts in range shifting species.

Reproductive and energetic costs of injury in the mangrove tree crab

“…Here we only examined 1 type of impact on reproduction -the impacts on actual reproductive products. Other aspects are also known to be important, such as the impacts of limb loss on ritualistic interactions that occur between individuals of this species during general encounters (Warner 1970, Cannizzo et al 2019) and potentially for reproductive interactions (Christy 1987). We also did not look at mechanisms of energetic constraints.…”

“…The mangrove tree crab Aratus pisonii is a marine neotropical species that is found abundantly associated with mangrove trees in the Atlantic from Brazil to Florida (Chace & Hobbs 1969), though it has recently expanded into salt marshes due to climate change (Riley et al 2014a). Subject to predation from birds and fish (Yeager et al 2016), as well as conspecific aggression (Cannizzo et al 2019), this species is known to readily employ autotomy as a habitatspecific anti-predator behavior (Johnston & Smith 2018). Research over the last several years has provided considerable knowledge of the reproduction and energetics of this species, making it an ideal study system for examining the impacts of limb loss on reproduction and the tradeoff between regeneration and reproductive effort.…”

“…We tested this for both the loss of claws and the loss of walking legs because each may influence food consumption differently. Missing claws may have direct effects due to their use in foraging; they may also have indirect effects because missing claws reduce the ability to engage in intraspecific aggression and thus restrict access to foraging grounds (Warner 1970, Cannizzo et al 2019), while walking legs may have indirect effects by hampering the ability of injured individuals to maneuver through mangrove canopies. We also test the hypothesis that the loss of walking legs or claws will reduce energy storage, either via reduced food intake or increased energy use for limb regeneration.…”

The impacts of mangrove range expansion on wetland ecosystem services in the southeastern United States: Current understanding, knowledge gaps, and emerging research needs

“…Along the Atlantic coast of North America, the northern range limit of mangrove tree crabs ( Aratus pisonii ) is currently in Georgia (Riley et al, 2014), which is north of mangrove forests’ current range limit in Florida. Interestingly, in the absence of mangrove trees, mangrove tree crabs can adapt to suboptimal novel marsh environments by: (1) shifting behavioral strategies from predator evasion (i.e., tree climbing) to autotomy (i.e., leg dropping) to optimize survival (Johnston & Smith, 2018), or (2) using anthropogenic structures like docks (Cannizzo & Griffen, 2018, 2019; Cannizzo et al, 2018, 2019, 2020). Anthropogenic structures such as bridges and docks may also provide habitat for juvenile goliath grouper in the northern Gulf of Mexico where adult spawning sites have been recently documented (Malinowski et al, 2019).…”

Ecological variation drives morphological differentiation in a highly social vertebrate

“…In social animals, variable ecological factors may directly affect social interactions by changing the costs and benefits of group living (Arnold & Owens, 1999; Curry, 1989; Koenig et al., 2011; Marshall et al., 2016). In addition, ecological variation may trigger adaptations in other phenotypic traits, which may, in turn, feed back on social organization (Cannizzo et al., 2019; Zuk et al., 1998). For example, parasite infections lead to changes in female red junglefowl's Gallus gallus comb size, which is accompanied with a shift in hierarchy so that infected females lose their dominance and consequently attain a lower social status (Zuk et al., 1998).…”