Cannibalism by large tadpoles of Rhinophrynus dorsalis (Anura: Rhinophrynidae)

In June 2014, we captured approximately 100 R. dorsalis tadpoles in a net from a seasonal wetland in Palo Verde National Park (10.3428 N, 85.3375 W) in N, 85.3375 W) in northwestern Costa Rica. While rearing the tadpoles in the laboratory, we observed five events in which larger tadpoles (Stage 26; Gosner, 1960) fed on conspecifics at earlier stages. At first, we interpreted this behaviour as scavenging. However, after observing more closely during two subsequent events, we noticed that the predated individuals were still alive. We were not able to observe interactions with tadpoles in older stages at this time due to tadpole mortality. Then, during the first week of the rainy season (May to November annually) on 23 May 2018, we collected approximately 300 Rhinophrynus dorsalis tadpolesUCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias de la Salud::Instituto Clodomiro Picado (ICP)UCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de Biologí

Evidence of maternal provisioning of alkaloid-based chemical defenses in the strawberry poison frog Oophaga pumilio

Many organisms use chemical defenses to reduce predation risk. Aposematic dendrobatid frogs sequester alkaloid-based chemical defenses from a diet of arthropods, but research on these defenses has been limited to adults. Herein, we investigate chemical defense across development in a dendrobatid frog, Oophaga pumilio. This species displays complex parental care: at hatching, mothers transport tadpoles to phytotelmata, and then return to supply them with an obligate diet of nutritive eggs for about six weeks. We collected eggs, tadpoles, juveniles, and adults of O. pumilio, and detected alkaloids in all life stages. The quantity and number of alkaloids increased with frog and tadpole size. We did not detect alkaloids in the earliest stage of tadpoles, but alkaloids were detected as trace quantities in nutritive eggs and as small quantities in ovarian eggs. Tadpoles hand-reared with eggs of an alkaloid-free heterospecific frog did not contain alkaloids. Alkaloids that are sequestered from terrestrial arthropods were detected in both adults and phytotelm-dwelling tadpoles that feed solely on nutritive eggs, suggesting that this frog may be the first animal known to actively provision post-hatch offspring with chemical defenses. Finally, we provide experimental evidence that maternally derived alkaloids deter predation of tadpoles by a predatory arthropod.Ministerio del Ambiente, Energía y Technologia/[10CR000024]/MINAET/Costa RicaThe Convention on International Trade in Endangered Species/[10CR000024]/CITES/Costa RicaUCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias de la Salud::Instituto Clodomiro Picado (ICP

Sexual dimorphism of the second-to-fourth digit length ratio (2D : 4D) in the Strawberry Poison Dart Frog (Oophaga pumilio) in Costa Rica

Chang (Stynoski), Jennifer LynnThe second-to-fourth digit ratio (2D : 4D) is a well-studied sexual dimorphism that likely arises as a result of prenatal androgenic effects on homeobox gene expression. This dimorphism has been found to exhibit interesting phylogenetic patterns in which females have larger ratios than males among most mammalian species and males have larger ratios than females in most avian and reptilian species. Digit ratio has not been measured in more basal taxa such as amphibians. In this study, 2D : 4D and snout–vent length (SVL) were measured in 40 male and 44 female adult Oophaga [=Dendrobates] pumilio frogs to investigate the existence and patterning of sexual dimorphism. The 2D : 4D of the rear feet varied significantly by sex with males having a larger ratio than females. The digit ratio of the front feet did not differ between the sexes. SVL or its interaction with sex did not affect 2D : 4D on any of the feet. These results indicate that 2D : 4D in an anuran is both sexually dimorphic and follows a pattern between the sexes similar to that of diapsid species. A potential application of 2D : 4D to environmental monitoring is also discussed.UCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de Biologí

Discrimination of offspring by indirect recognition in an egg-feeding dendrobatid frog, Oophaga pumilio

Offspring discrimination, the differential treatment of offspring and unrelated young, functions in numerous animal taxa to ensure that vital and costly parental care behaviours are appropriately directed. Discrimination can be facilitated either by direct (phenotypic) recognition of offspring or by indirect (nonphenotypic) recognition of offspring location. Offspring discrimination and recognition mechanisms have not been identified in an amphibian. In the strawberry poison frog, Oophaga pumilio, a dendrobatid frog with obligatory maternal provisioning behaviour, I tested whether mothers discriminate between offspring and unrelated young, whether they use direct or indirect recognition cues, and whether prior parental investment plays a contextual role in the differential treatment of young. Mother frogs utilized tadpole-rearing cups attached to tree trunks in wet tropical forest. After manipulating the identity, location and/or age of tadpoles in cups, I determined whether maternal provisioning behaviour was maintained by measuring tadpole growth and development. Mothers provisioned young regardless of tadpole identity, but were sensitive to location and did not provision tadpoles that were moved 2 cm to an adjacent cup. When given a choice between related and unrelated tadpoles in originally chosen or adjacent cups, mothers discriminated by location, but not by relatedness. Maternal provisioning behaviour persisted when a tadpole provisioned for 10 days was replaced with either an age-matched or newly hatched unrelated tadpole, so direct offspring recognition does not appear to be dependent on prior parental investment. Together, these results provide strong evidence that mother O. pumilio use indirect recognition cues to discriminate between offspring and unrelated offspring.Organization of Tropical Studies/[]/OTS/Estados UnidosInstitutional Animal Care and Use Committee/[]/IACUC/Estados UnidosUCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de Biologí

Maternally derived chemical defenses are an effective deterrent against some predators of poison frog tadpoles (Oophaga pumilio)

Parents defend their young in many ways, including provisioning chemical defences. Recent work in a poison frog system offers the first example of an animal that provisions its young with alkaloids after hatching or birth rather than before. But it is not yet known whether maternally derived alkaloids are an effective defence against offspring predators. We identified the predators of Oophaga pumilio tadpoles and conducted laboratory and field choice tests to determine whether predators are deterred by alkaloids in tadpoles. We found that snakes, spiders and beetle larvae are common predators of O. pumilio tadpoles. Snakes were not deterred by alkaloids in tadpoles. However, spiders were less likely to consume mother-fed O. pumilio tadpoles than either alkaloid-free tadpoles of the red-eyed treefrog, Agalychnis callidryas, or alkaloid-free O. pumilio tadpoles that had been hand-fed with A. callidryas eggs. Thus, maternally derived alkaloids reduce the risk of predation for tadpoles, but only against some predators.University of Miami/[NSF-OISE1114218]/UM/Estados UnidosUCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de Biologí

Developmental morphology of granular skin glands in pre-metamorphic egg-eating poison frogs

Parents in many taxa, including insects, mol- luscs, fish, snakes, and amphibians provision chemical defences, such as peptides, steroids, or alkaloids to their offspring to reduce the risk of predation. In most cases, those defences are transferred to offspring in the egg and gradually diminish throughout the larval period. Adult poi- son frogs sequester alkaloid-based defences from arthro- pod prey in granular skin glands. In at least one poison frog, Oophaga pumilio, mother frogs intermittently feed tadpoles until metamorphosis with nutritive eggs contain- ing those alkaloid-based defences. However, alkaloids are not detected in tadpoles until they reach the middle stages of larval development. Here, we investigate the histology of a developmental series of O. pumilio tadpoles to deter- mine whether their ontogenetic alkaloid profile coincides with granular gland development. Our findings suggest that alkaloid sequestration in tadpoles is delineated by the dif- ferentiation of rudimentary granular skin glands in epithe- lial tissue. The timing of differentiation of granular glands in this species coincides with other anurans. Thus, provisioning of chemical defences to offspring is likely constrained by developmental timing of derived structures that can effectively store those toxic or noxious compounds.National Science Foundation/[IOS-1528866]/NSF/Estados UnidosUCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de Biologí

Differences in escape behavior between a cryptic and an aposematic litter frog

Clay models have been used to investigate the relative antipredator effectiveness of cryptic and of aposematic coloration in litter frogs, but such studies do not account for possible differences in prey escape behavior. We examined the escape behaviors of two litter frogs, the cryptic Craugastor bransfordii and the brightly colored and toxic Oophaga pumilio, in response to a human predator. For all individuals, we measured the distance between the frog and the observer at the instant of flight and the distance between frog’s initial and final positions in the field. The cryptic C. bransfordii had a shorter flight initiation distance than did nonvocalizing individuals of the brightly colored O. pumilio. In addition, we noted that vocalizing O. pumilio males had a shorter flight initiation distance than did either nonvocalizing male or female O. pumilio. These findings demonstrate that a cryptic and an aposematic litter frog differ in their escape response to a predator. These results also suggest that, at least in male O. pumilio, a trade-off may exist between predator avoidance and reproductive success via territorial defense and mate attraction.Ministerio del Ambiente y Energía/[]/MINAE/Costa RicaUniversity Fellowship/[]//Reino UnidoOrganization for Tropical Studies/[]/OTS/Estados UnidosUCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias de la Salud::Instituto Clodomiro Picado (ICP

Rhaebo haematiticus (litter toad) and Craugastor fitzingeri (Fitzinger's rain frog) reproductive behavior

C. fitzingeri was observed in amplexus with a large female R. haematiticus at Sarapiquí, Costa RicaUCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de Biologí

Tadpole begging reveals high quality

Parents can benefit from allocating limited resources non randomly among offspring, and offspring solicitation (i.e. begging) is often hypothesized to evolve because it contains information valuable to choosy parents. We tested the predictions of three ‘honest begging’ hypotheses – Signal of Need, Signal of Quality and Signal of Hunger – in the tadpoles of a terrestrial frog (Oophaga pumilio). In this frog, mothers provision tadpoles with trophic eggs, and when mothers visit, tadpoles perform a putative begging signal by stiffening their bodies and vibrating rapidly. We assessed the information content of intense tadpole begging with an experimental manipulation of tadpole condition (need/quality) and food deprivation (hunger). This experiment revealed patterns consistent with the Signal of Quality hypothesis and directly counter to predictions of Signal of Need and Signal of Hunger. Begging effort and performance were higher in more developed and higher condition tadpoles and declined with food deprivation. Free-living mothers were unlikely to feed tadpoles of a non begging species experimentally cross-fostered with their own, and allocated larger meals to more developed tadpoles and those that vibrated at higher speed. Mother O. pumilio favour their high- quality young, and because their concurrent offspring are reared in separate nurseries, must do so by making active allocation decisions. Our results suggest that these maternal choices are based at least in part on offspring signals, indicating that offspring solicitation can evolve to signal high quality.Louisiana Board of Regents/[LEQSF‐EPS(2013)‐PFUND‐332]//Estados UnidosNational Science Foundation/[1146370]/NSF/Estados UnidosUCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de Biologí

Larval aggression is independent of food limitation in nurseries of a poison frog

Aggression between nurserymates is common in animals and often hypothesized to result from proximate resource limita- tion. In numerous terrestrial frogs, larvae develop in phytotelmata, tiny water bodies where resources are scarce and competition, aggression, and cannibalism are all common between individuals sharing these nurseries. In some species, mothers provision phytotelm-bound young with trophic eggs, a strategy that compensates for low nutrient availability and could allow mothers to reduce costly aggression and cannibal- ism among nurserymates. We tested this hypothesis using strawberry poison frog (Oophaga pumilio) tadpoles, staging secondary depositions in arenas occupied by residents that had either been food deprived or fed ad libitum. Resident tadpoles were nearly all aggressive and most killed intruders, but aggression was unrelated to resident food deprivation. Unlike most related frogs studied, O. pumilio residents did not cannibalize their victims. This result supports the hypothesis that proximate food limitation and aggression can be independent.Louisiana Board/[LEQSF-EPS(2013)-PFUND-332]//Estados UnidosNational Science foundation/[1146370]/NFS/Estados UnidosUCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias de la Salud::Instituto Clodomiro Picado (ICP