Blind toads in paradise: the cascading effect of vision loss on a tropical archipelago

Abstract

On the archipelago of Fernando de Noronha, nearly half of the individuals in the invasive population of Cururu toads have mouthpart, limb or eye deformities. Among these, a subset of adult toads is completely blind or has just one functional eye. In this study, we examined the consequences of this vision loss in relation to feeding and reproductive biology. Blind toads were handicapped relative to normal toads, whereas the half-blind individuals were intermediate. In contrast to the expected active hunting mode used by normal toads, blind toads searched for prey using a sit-and-wait foraging strategy. The small sample of blind toads (n = 4) had no stomach contents. However, eight half-blinded and 86 sighted animals presented stomach contents, and differed in general diet profile. Body condition as well as reproductive effort increased according to the number of functional eyes. Therefore, we suggest that shifts in feeding and hunting, as a consequence of vision loss, influence diet, with subsequent impact on overall body condition and reproductive effort. A cascade effect of this kind has not been previously reported and provides insightful data related to behavioral plasticity and reproductive fitness.

Reporting on a half-blind Cane toad Rhinella marina (Anura: Bufonidae) from the island of Montserrat

“…Similar eye deformities in toads have also been reported in at least two other island systems: firstly on the R. marina population in Bermuda (Bacon et al, 2006), and later on a Cururu toad (Rhinella jimi) population introduced to the island of Fernando de Noronha (Brazil) (Toledo & Ribeiro, 2009;Tolledo & Toledo, 2015). Although toads show high rates of malformations in both cases, the causes have yet to be confirmed.…”

“…Ocular abnormalities (e.g. Boon-Hee et al, 2013;Fernández-Loras et al, 2016;Tolledo & Toledo, 2015) are amongst the least frequently reported cases (Reeves et al, 2013;Laurentino et al, 2015), and can be the result of many factors such as environmental contaminants (metals and petroleum hydrocarbons) (Bacon et al, 2013), pesticides (Gurushankara et al, 2007), emerging diseases (Burton et al, 2008) and predation (Lannoo, 2008).…”

Perspectives on invasive amphibians in Brazil

“…g ., chemical pollutants) or intrinsic handicaps such as inbreeding depression (see [ 78 , 79 ]). Rhinella jimi has been established in Fernando de Noronha for about 100 years and these toads are thriving despite showing high prevalence of multiple types of abnormalities [ 78 , 133 ]. This is another example of how invasive species can benefit from the lack of local competitors and predators in oceanic islands [ 78 , 79 ].…”

Limb abnormalities in Peltophryne florentinoi (Anura: Bufonidae) from Cuba

“…These authors considered that inbreeding would lead to the same types of anomalies in all affected individuals, not to the heterogeneous observed. However, the high frequency of malformations detected in insular populations of toads from Brazil, ranging from mouthpart anomalies, limb reduction to loss of eyes, has been associated with genetic structure and inbreeding (Toledo and Ribeiro 2009, Tolledo and Toledo 2015, Bessa-Silva et al 2016, Reboucas et al 2019. The small population of Zapata's Toad is restricted to a few localities from the eastern part of the Zapata region, Matanzas province to the east of Cienfuegos City, Cienfuegos Province, associated with coastal microphyllous evergreen forest with different level of human perturbation.…”