Making Friends: Social Attraction in Larval Green and Golden Bell Frogs, Litoria aurea

Abstract

Socio-ecological models combine environmental and social factors to explain the formation of animal groups. In anurans, tadpole aggregations have been reported in numerous species, but the factors driving this behaviour remain unclear. We conducted controlled choice experiments in the lab to determine whether green and golden bell frog (Litoria aurea) tadpoles are directly attracted to conspecifics (social factors) in the absence of environmental cues. Using repeated measures, we found that individual tadpoles strongly preferred associating with conspecifics compared to being alone. Furthermore, this preference was body size dependent, and associating tadpoles were significantly smaller than non-associating tadpoles. We suggest that small tadpoles are more vulnerable to predation and therefore more likely to form aggregations as an anti-predator behaviour. We demonstrate that tadpoles present an ideal model system for investigating how social and ecological factors influence group formation in vertebrates.

The role of biotic and abiotic cues in stimulating aggregation by larval cane toads (Rhinella marina)

“…This relatively shallow water depth was deemed appropriate as R. marina tadpoles often occur in shallow water (Crossland & Shine, 2011), and is also consistent with the protocols of similar experiments (Leu et al, 2013;Sontag et al, 2006;Waldman & Adler, 1979;Wassersug & Hessler, 1971).…”

“…Except where stated, the following experiments were conducted in evenly lit arenas filled with aged water at a depth of 30 mm and a temperature of 25°C, which is within the thermal range measured in natural ponds in the Northern Rivers region (Wijethunga et al., ). This relatively shallow water depth was deemed appropriate as R. marina tadpoles often occur in shallow water (Crossland & Shine, ), and is also consistent with the protocols of similar experiments (Leu et al., ; Sontag et al., ; Waldman & Adler, ; Wassersug & Hessler, ).…”

“…Protection from predators is a well‐known benefit of aggregation (Le Roux, Cherry, & Manser, ; Leu et al., ) and animals often use chemical information from wounded conspecifics to predict the risk of predator attack (Goodale, Beauchamp, Magrath, Nieh, & Ruxton, ; Hagman et al., ). In response to chemical cues from an injured conspecific, tadpoles in our experiments modified their swimming speed (indicating that tadpoles recognized the cue) but did not aggregate.…”

“…An “aggregation” can be defined as any localized assemblage of individuals where the density of individuals is higher than in the contiguous area (Camazine, ; Jeanson et al., ). Aggregation occurs in organisms ranging from vertebrates to bacteria (Ward & Webster, ), and can entail both costs (e.g., competition for resources and mates, predator attraction, parasite, and disease transmission) and benefits (dilution of predation risk, enhanced foraging, increased vigilance, and predator confusion) (Beiswenger, ; Dall, Giraldeau, Olsson, McNamara, & Stephens, ; Foster & Treherne, ; Hamilton, ; Leu, Whiting, & Mahony, ; Pulliam, ; Sansom, Cresswell, Minderman, & Lind, ; Sontag, Wilson, & Wilcox, ). However, proximate cues for aggregation are poorly understood for many organisms (Sempo, Depickère, & Detrain, ).…”

“…Generally, groups form in response to two types of stimuli: biotic and abiotic. Inter‐individual social attraction is a common mechanism of group formation and maintenance, along with responses to other biotic factors including predator cues and food (Alexander, ; Grunbaum & Okubo, ; Leu et al., ). Conversely, aggregations also can arise as a by‐product of shared preferences for specific (and localized) habitat features (Sempo, Canonge, Detrain, & Deneubourg, ).…”