Evolution of treefrogs' calls in tropical islands might be under directional selection

Abstract

Animals that present migration restrictions are especially interesting to study isolation effects in the context of island biogeography theory. Among these effects, behavioral traits are one of the least studied subjects. The treefrog Boana albomarginata presents gigantism in some Atlantic islands and, therefore, examining its advertisement calls may be an opportunity to test the Island Rule with a behavioral trait. Hence, we compared calls, body and tympanum sizes of populations of this species in Brazilian islands and mainland sites. We tested if call frequencies of island individuals differed from mainland ones, also considering the influence of body size and its relationship with tympanum diameter. One of the island population had larger body size and lower call frequencies than any other populations. We suggest that to be a result of directional selection. We also observed lack of correlation between body size and advertisement call frequencies in some populations, implying that males and females cannot use calls as a proxy of the calling male's size, which may indicate a rare case of relaxed selection. Therefore, this is the first evidence of relaxed selection in animal communication, as a consequence of recent insularity.

When Rensch meets Foster: insular gigantism may reduce sexual dimorphism in anurans

“…Although this increased male size might be the consequence of directional selection (e.g. higher competition between males, as highlighted in Reboucas et al 2020), this led to a reduction in the SSD. More broadly, across anurans, we highlighted that decreased SSD with increasing body size was strongly linked to body size changes in male individuals, but not in females.…”

“…highlighted in Reboucas et al 2020), this led to a reduction in the SSD. More broadly, across anurans, we highlighted that decreased SSD with increasing body size was strongly linked to body size changes in male individuals, but not in females.…”

“…Additional factors are known to influence the validity of the Island rule (Lomolino 1985, Palkovacs 2003, Meiri et al 2008, Rebouças et al 2018), supporting the hypothesis that size modification on islands can be population‐ and/or species‐specific (Benítez‐López et al 2021). For instance, individuals that have colonized OI could have, by chance, already been larger, leading to a genetic drift (founder effect, Barton and Charlesworth 1984; as highlighted in Reboucas et al 2020). In addition, ecological island‐specific factors such as reduced predation pressure, competition and/or resources availability, could influence body size.…”

Midges not only sucks, but may carry lethal pathogens to wild amphibians

“…Individuals of Corethrella spp. were collected during a fieldtrip to the municipality of Mogi das Cruzes, state of São Paulo, Brazil (23°29'14.8" S, 46°10'14.6" W), using a frog‐call trap with the advertisement calls of Boana albomarginata (Hylidae, Anura), which is widespread in the Atlantic forest and have call frequencies roughly between 1 and 3.5 kHz (Rebouças et al, 2020). A single trap, placed in a pond margin, was active for 30 minutes from 18:00 to 22:00, from 23 to 25 September 2019 (total sampling effort = 1h30 min).…”

“…have call frequencies roughly between 1 and 3.5 kHz(Rebouças et al, 2020). A single trap, placed in a pond margin, was active for 30 minutes from 18:00 to 22:00, from 23 to 25 September 2019(total sampling effort = 1h30 min).…”