A Surprising Twist in Arachnid Parenting
When most people think of parental care among arthropods, insects and true spiders dominate the conversation. Yet a lesser‑known group of arachnids—harvestmen, often called “daddy longlegs”—is turning that assumption on its head. Some species entrust egg‑guarding to the mother, while in a striking minority the father assumes the responsibility. Because paternal care is rare in the animal kingdom, understanding how and why it evolved in harvestmen offers a unique window into the forces that shape family life across evolution.
Harvestmen: Not True Spiders
Although harvestmen resemble spiders at a glance, they belong to a separate order (Opiliones). They lack silk glands and venom, and their body plan is distinct. This biological distance makes them especially valuable for comparative studies: any pattern of parental investment that diverges from the spider model can highlight alternative evolutionary routes.
Citizen Science Powers the Discovery
The breakthrough came from an unexpected source—photos uploaded by everyday nature enthusiasts to the platform iNaturalist. Researchers from the Smithsonian Tropical Research Institute and the University of São Paulo sifted through roughly 24,000 images, pinpointing 53 harvestmen species that displayed clear evidence of parental behavior. By cross‑referencing these visual records with field observations and laboratory data from 19 scientists across five Latin‑American countries, the team expanded reliable information from 40 to 85 species, more than doubling the known dataset.
Evolutionary Insights: Mothers vs. Fathers
Armed with this enriched dataset, the scientists reconstructed a phylogenetic tree encompassing 165 species from nine families. The analysis revealed two distinct evolutionary pathways. Maternal care appeared only in lineages that had previously shown no parental involvement, suggesting a sudden acquisition of the trait. Paternal care, however, emerged through two routes: in some lineages it arose directly from a non‑caring ancestor, while in others it evolved from species that originally exhibited maternal care. This dual origin hints that different ecological or social pressures can independently favor male egg‑guarding.
Parental Care Can Appear and Disappear
The study also documented frequent loss of parental behavior. When care vanished, many harvestmen compensated by hiding their eggs under bark, within crevices, or by camouflaging them with surrounding debris. Such strategies reduce the need for prolonged attendance, demonstrating that the absence of a caregiver does not automatically translate into unprotected offspring.
Implications for Future Research
Beyond harvestmen, the research underscores the power of citizen science. A single snapshot taken for personal enjoyment can capture a behavior that has never been described by professionals. By aggregating these observations, scientists can accelerate discoveries across taxa, from insects to vertebrates. The authors argue that similar methodologies could illuminate other complex behaviors—courtship rituals, migration routes, or even disease dynamics—whenever the public contributes high‑quality, geotagged imagery.
Source: https://scientias.nl/bij-deze-spinachtige-dieren-zorgen-soms-de-vaders-voor-de-eieren/
