Developments in Amphibian Parental Care Research: History, Present Advances, and Future Perspectives

Abstract

Despite rising interest among scientists for over two centuries, parental care behavior has not been as thoroughly studied in amphibians as it has in other taxa. The first reports of amphibian parental care date from the early 18th century, when Maria Sibylla Merian went on a field expedition in Suriname and reported frog metamorphs emerging from their mother's dorsal skin. Reports of this and other parental behaviors in amphibians remained descriptive for decades, often as side notes during expeditions with another purpose. However, since the 1980s, experimental approaches have proliferated, providing detailed knowledge about the adaptive value of observed behaviors. Today, we recognize more than 30 types of parental care in amphibians, but most studies focus on just a few families and have favored anurans over urodeles and caecilians. Here, we provide a synthesis of the last three centuries of parental care research in the three orders comprising the amphibians. We draw attention to the progress from the very first descriptions to the most recent experimental studies, and highlight the importance of natural history observations as a source of new hypotheses and necessary context to interpret experimental findings. We encourage amphibian parental care researchers to diversify their study systems to allow for a more comprehensive perspective of the behaviors that amphibians exhibit. Finally, we uncover knowledge gaps and suggest new avenues of research using a variety of disciplines and approaches that will allow us to better understand the function and evolution of parental care behaviors in this diverse group of animals.

Olfaction across the water–air interface in anuran amphibians

“…Breeding in small temporary ponds comes with the advantage of less predation but also lower food abundance (Wassersug et al 1981 ). This favored the evolution of parenting behavior and food provisioning in many tropical frog species (Wells 2007a ; Brown et al 2008 ; Roland and O’Connell 2015 ; Schulte et al 2020 ). In the Taiwanese tree frog Chirixalus eiffingeri , tadpoles become more active when exposed to water conditioned by a female frog (Kam and Yang 2002 ), possibly in the anticipation of trophic eggs laid by the female.…”

Alloparental care in glassfrogs: males care for unrelated clutches only when associated with their own

“…Anurans show elaborate and conspicuous social and reproductive behaviors, making them a natural model system to investigate mating and parental care 20 , 21 . In the glassfrog family Centrolenidae, males of some species of the genera Hyalinobatrachium and Centrolene attend clutches deposited on the undersides of leaves above water 22 .…”

Correlated evolution of parental care with dichromatism, colour, and patterns in anurans

“…Amphibians are a species-rich group [21] that are colourful [22], dichromatic [19], and show some of the most diverse forms of caregiving behaviours [23]. Parental care behaviour has been documented in approximately 20% of the extant 8200 species in amphibians [24][25][26][27] and is an integral component in the classification of the reproductive modes in this group [23,28].…”

“…Despite the diversity and complexity of reproductive modes (~40 distinct reproductive modes; [27]), our understanding of parental care evolution in amphibians is still lagging compared to that of other vertebrate groups [24,29]. What is clear is that caregiving behaviours among anurans are phylogenetically widespread and converge between distantly related lineages [25].…”

“…Across anuran species, care-giving behaviours vary in duration and intensity [23,25,30,31] as well as form and complexity [26]. Among the nine classified categories of parental care in anurans [See: 24], egg attendance, wherein adults defend, clean, or hydrate eggs is the simplest and most frequently observed form [23,24,26] whereas viviparity is complex, requiring specialised anatomical and physiological adaptations that are infrequently observed [24,26]. Studies have found that parental care behaviour in anurans is correlated with multiple ecological factors, including breeding pool size and terrestrial reproduction [25,32,33] that are strong indicators of the risks to adults and young by predators in both the aquatic and terrestrial habitats.…”