# Trans‐Generational Morphological Trait Plasticity in Parthenogenetic Offspring of Two Brachionus dorcas Morphotypes Induced by Asplanchna Kairomones

## TL;DR

This study shows how two types of rotifers respond differently to environmental signals over multiple generations, affecting their body size and spine length in distinct ways.

## Contribution

The study reveals divergent trans-generational defense strategies in rotifer morphotypes in response to kairomones, offering new insights into adaptive developmental plasticity.

## Key findings

- SS rotifers showed a 'rapid and moderate response' with increased body size and spine elongation from early generations.
- LS rotifers exhibited a 'slow and extreme defense' with delayed spine elongation and maximum spine length in later generations.
- The morphotypes' different strategies may stem from evolutionary trade-offs involving resource allocation and environmental predictability.

## Abstract

We compared trans‐generational (F0–F12) morphological trait plasticity induced by Asplanchna kairomones between two
Brachionus dorcas
morphotypes (long‐posterior spines, LS; short‐posterior spines, SS) along with life‐table parameters of the non‐induced morphotypes. Under control conditions, SS rotifers tended to show higher fertility and smaller body size than LS rotifers. Low kairomone concentrations (50 and 200 ind./L) tended to increase body size in SS offspring, while exposure to 50, 200, and 800 ind./L kairomones induced spine elongation in both morphotypes, with posterolateral spine (PS) length increasing with kairomone concentration. Compared to the F0 generation, offspring of both morphotypes in unexposed controls showed generational fluctuations in body size; LS offspring exhibited shortening or no change in anteromedian spine (AMS) and anterolateral spine (ALS) lengths, while SS offspring showed elongation or no change in these spine lengths and PS length. Across all kairomone treatments, significant elongation of AMS and ALS in LS offspring was typically observed only in later generations, whereas SS offspring exhibited significant elongation from F1 through F12; LS offspring showed significant PS elongation from F2 through F12, with maximum lengths in the later generations (F5–F12), while SS offspring showed significant PS elongation from F1 through F12, peaking in early generations (F2–F4). Notably, the multi‐generational mean PS length in SS offspring remained significantly shorter than that in LS offspring under each kairomone treatment. Overall, SS offspring appeared to employ a synergistic defense combining increased body size and spine elongation favoring a “rapid and moderate response,” whereas LS offspring exhibited a “slow and extreme defense” strategy. These divergent strategies may result from evolutionary trade‐offs involving resource allocation, environmental predictability, and genetic constraints.

We compared life‐table parameters and trans‐generation (F0–F12) morphological developmental plasticity induced by Asplanchna kairomones between two
Brachionus dorcas
morphotypes (long‐posterior spines, LS; short‐posterior spines, SS). The results revealed that the SS offspring employed a synergistic defense combining increased body size and spine elongation, and favored a “rapid and moderate response,” while the LS offspring exhibited a “slow and extreme defense” strategy, which likely resulted from evolutionary trade‐offs involving resource allocation, environmental predictability, and genetic constraints. This study provides new insights into the evolutionary strategies of adaptive developmental plasticity and the ecological mechanisms of morphological polymorphism in rotifers, and Oikos is the best platform to publish this article.