On the distinctive call of a threatened phenotype of Allobates femoralis (Anura: Aromobatidae) and its recognition by allopatric conspecific males

Abstract

ABSTRACT. The brilliant-thighed frog [Allobates femoralis (Boulenger, 1884)] is distributed across the Amazon basin and aggregates several allopatric evolutionary lineages, some of which present variation in their advertisement calls. In 2009, an unregistered call phenotype was discovered in the region of Altamira and Vitória do Xingu, State of Pará, Brazil, where males emit advertisement calls formed by six notes, diff ering from the typical four-note calls described for other A. femoralis populations. In this study, we describe in detail these untypical calls. Additionally, we test whether the aggressive responses of males of a 4-note reference population (Reserva Ducke -RFAD, in Manaus, States of Amazonas) is diff erential towards the 6-note calls of males recorded in Altamira (Pará State), and towards 4-note calls recorded in one location at the Tapajós-Xingu interfl uve (Belterra, Pará State), and in RFAD. Playback experiments were conducted between 2011-2012, and used standardized stimuli produced from natural call recordings. A total of 30 independent experiments were conducted, 10 for each stimuli class. We measured the phonotaxis of focal males in relation to the loudspeaker, considering the time to orientation and the time to approach the loudspeaker. We found that not all A. femoralis males at RFAD promptly recognize calls from males recorded in Altamira. However, when considering only males who approached the loudspeaker, diff erences in aggressive reactions were not seen between stimuli classes. Our fi ndings show that the ability to recognize calls from Altamira as belonging to co-specifi c males is not universal among males at RFAD. The new A. femoralis phenotype occurs in areas potentially impacted by the Belo Monte hydroelectric complex and complementary studies indicate that no gene fl ow exists between this group and A. femoralis from adjacent regions. Hence, developments in Altamira may put this incipient speciation process at risk.