Diversification of Leech Proboscis Structure According to Prey Ingestion Behavior

Abstract

Background Adaptive radiation is a phenomenon in which various organs, depending on their diet and circumstance, are diversified morphologically or functionally as animals adapt to the environment. Although previous studies on changes caused by various external pressures have been well studied, the evidence for variation in invertebrates is not well known. We used freshwater leeches as an invertebrate model to observe their specific trophic niche and diversity of ingestion organ. Our results show convergent evolution according to structural changes through a representative species Alboglossiphonia sp., and the origin from common ancestor due to the remaining fluid ingestion behavior of the larval stages as a vestige.Results We identified the feeding behavior of rhynchobdellid leeches, which have the proboscis. Alboglossiphonia sp. swallows the entire prey using its proboscis, whereas proboscis leeches exhibit typical fluid-sucking behavior. We observed that proboscis of fluid-sucking leeches encompasses compartmentalized and dense muscle layers. In contrast, macrophagous leeches have relatively simple esophagus structures. To address whether the different feeding behaviors were intrinsic, we investigated the behavioral pattern and muscle arrangement in the earlier developmental stage of rhynchobdellid leeches. Interestingly, juveniles of the macrophagous leech as well as fluid-sucking leeches have the proboscis with the compartmentalized muscle layers and exhibit fluid-sucking behaviorsConclusions Animals have adapted various ways to obtain the energy needed for their survival. Diversification and evolution of ingestion methods across species further exhibit the functional morphology of the ingestion organ. However, information on ingestion behavior and internal structure is still lack and unclear, especially in invertebrate models. Our results suggest that the proboscis leeches have originated from the common fluid-sucking glossiphoniid ancestor and species diversification has led to modifications in the structure of the feeding tube. Together, leeches represent a comparative model for esophagus development according to the ingestion pattern based on diverse muscular arrangement in proboscis.