Lala, K. | Search bioRxiv

bioRxiv2026

Beneficial microbes may have favoured the evolution of adaptive immunity

Vertebrate adaptive immunity has long been considered uniquely advantageous for its capacity to recognise and remember a wide diversity of molecular targets, potentially conferring lasting defence from any threatening microbe. However, over the last two decades, results from comparative immunology have called into question the relative benefits of vertebrate adaptive immunity as a defence mechanism, raising the possibility of alternative evolutionary explanations. For instance, the hypothesis that managing the diverse and often beneficial host-microbiota associations characteristic of the vertebrate gut may have favoured the evolution of adaptive immunity. Here, we use individual-based simulations to investigate co-evolutionary interactions between hosts and their microbiota and the implication for the evolution of adaptive immunity. We focus on the capacity of adaptive immunity to produce and modify a diverse repertoire of immune receptors by using somatic variation and selective clonal reinforcement, in combination with a reinforcement bias from the innate immune system. Strikingly, we find that a high diversity of rapidly evolving parasites is insufficient to favour the evolution of adaptive immunity. Instead, our findings suggest that neutral and beneficial microbes can play a crucial role in weakening selection on innate immune defence against parasites, in favour of the exploitation of beneficial microbes. In turn, this facilitates the emergence of adaptive immunity as a mechanism reducing the risk associated with infrequent parasite infections while exploiting beneficial microbes. In addition, we show that adaptive immunity can subsequently alter selection affecting both innate immune defence and microbe evolution, such that its loss becomes increasingly unlikely with evolutionary time. Together, these results suggest that simultaneous interactions with diverse mutualists and parasites is a compelling selective explanation for the emergence and maintenance of adaptive immunity.

evolutionary biology↗

bioRxiv2025

Tracking morphological development in stony corals

The shape of reef-building corals largely determines how they interact with their environment and the ecosystem services they provide. However, morphology is not fixed. As corals grow and develop from singular polyps to mature adult colonies, they experience pronounced changes in their morphology. This developmental trait variation remains poorly quantified in corals, despite their importance as ecosystem engineers. To address this gap, we used photogrammetry to track the morphological development of wild coral colonies across six size-independent metrics designed to capture variation in volume compactness, surface complexity, and top-heaviness. Size-trait models and analyses of colony movement through morphological trait space revealed that small colonies shared compact morphologies and only later diverged along growth-form-specific developmental trajectories. Massive corals largely retained stable shapes as they grew, whereas non-massive colonies became less compact, more top-heavy, and in most cases, more complex. Despite these differences, there was still overlap between growth forms in their developmental trajectories through morphospace. These findings highlight that traditional categorical growth forms mask important developmental variation, particularly early in coral ontogeny. By applying a quantitative trait-based framework, this study improves understanding of coral morphological development and provides a foundation for linking individual growth trajectories to broader reef ecosystem dynamics.

ecology↗