Science1 publisher2 min readPublished
Reared alone, toad tadpoles hung back from siblings and strangers alike
Kazuko Hase raised Japanese common toad tadpoles alone or with twenty siblings, then timed which tadpoles they swam toward. Their choices tracked how they had been raised; kinship made no difference.
The Scientist · Science desk
What happened
- Kazuko Hase at Kyoto University tested whether Japanese common toad tadpoles prefer the company of siblings, in work published in the journal Animal Cognition.
- She reared the tadpoles in a design that crossed two water types, tap and pond, with two rearing conditions: a group of 20 siblings, or alone.
- Two weeks after hatching, each tadpole was offered a sibling and a nonsibling at the same time, and its movements were tracked for 60 minutes across sibling, nonsibling and neutral zones.
- None of the tadpoles preferred siblings, whatever water they grew up in and whatever company they had, which Hase reports as lower kin recognition than in other tadpole species.
- The tadpoles raised alone were slower to approach any other tadpole, sibling or stranger, and spent more of the test in the neutral zones.
Compiled by The ScientistSomething wrong?How this is made
Why it matters
- constraint The kinship half of this result is a null, so a general claim that peers outweigh family in tadpole sociality needs a study powered to find kin preference that still fails to find it.
- precedent The next test of the microbial-odour idea has to get past a crossed design in which pond water made no measurable difference, which pushes the work toward more animals or finer measures than time in a zone.
- decision A captive-rearing programme reading this would spend its attention on keeping larvae with peers; the water they grew up in left their behaviour unchanged.
The paper reports an effect and a null. Whether a tadpole grew up with peers changed how close it got to other tadpoles [7]. Kinship made no difference Hase could measure, under any rearing condition [6]. The second finding is a failure to detect, and what it is worth depends on how many animals stood behind it. The four sibling groups came from four egg masses collected around the University of Tokyo's Botanical Gardens, and each mass was treated as a set of siblings [3]. Crossing those four families with the four rearing conditions makes sixteen family-by-treatment cells [14][15]. The phys.org account does not report how many tadpoles filled them, or how big the isolation effect was [16].
Tadpoles gather to avoid predators [12], and the choice test is a proxy for that gathering. Isolated tadpoles spent more of the hour in the neutral zones [7]. Time in a zone measures position. A tadpole that swims less, or that stays near where it was dropped, accumulates neutral-zone time with no preference involved, so telling a dulled social approach apart from a dulled swim needs an activity measure alongside the zone times.
The title of the paper states the finding as "Social isolation, rather than kinship, influences association behavior in toad tadpoles (Bufo formosus)" [2]. Calling that sociality acquired goes a step past what one test at one age supports. Each tadpole was assessed two weeks after hatching [5]. An isolate that approaches less on day 14 might approach normally on day 30. This design ends at two weeks.
The water arm was aimed at a specific idea. Recent work has suggested that microorganisms influence communication through animal body odours, and microbe-rich pond water has therefore been raised as a possible influence on social behaviour [13]. Tap and pond water ran inside both rearing conditions, and Hase reported no significant effect of the water environment, with the isolation result holding across both [8]. So the most direct version of that prediction fails here, in one species, at one age.
"Unlike closely related species in which kin recognition has been confirmed during social aggregation, I was surprised to find that it is not essential for social aggregation in the Japanese common toad," said Hase, who is the paper's sole author and its corresponding author [9][17]. On why the species matters to her, she said, "The Japanese common toad is facing the threat of extinction, so we want to help protect them" [10]. She added, "I am also delighted that these toad tadpoles that I love so much are contributing to scientific progress" [11].
What to watch
- What the paper reports for tadpoles per cell, the size of the isolation effect, and whether swimming activity was scored alongside time in zones.
- A test of kin discrimination at a later larval stage would show whether the null is about age at testing or about the species.
- Whether captive-rearing work on the threatened Bufo formosus adopts group rearing on the strength of results like this.