A tale of two leeches: Toward the understanding of the evolution and development of behavioral neural circuits

Abstract

In the animal kingdom, behavioral traits encompass a broad spectrum of biological phenotypes that have critical roles in adaptive evolution, but an EvoDevo approach has not been broadly used to study behavior evolution. Here, we propose that, by integrating two leech model systems, each of which has already attained some success in its respective field, it is possible to take on behavioral traits with an EvoDevo approach. We first identify the developmental changes that may theoretically lead to behavioral evolution and explain why an EvoDevo study of behavior is challenging. Next, we discuss the pros and cons of the two leech model species, Hirudo, a classic model for invertebrate neurobiology, and Helobdella, an emerging model for clitellate developmental biology, as models for behavioral EvoDevo research. Given the limitations of each leech system, neither is particularly strong for behavioral EvoDevo. However, the two leech systems are complementary in their technical accessibilities, and they do exhibit some behavioral similarities and differences. By studying them in parallel and together with additional leech species such as Haementeria, it is possible to explore the different levels of behavioral development and evolution.

A premotor microcircuit to generate behavior-specific muscle activation patterns in Drosophila larvae

“…Studies of different animal models have provided valuable insights on how motor circuits produce diverse motor outputs and how different muscles are coordinated during execution of a given motor behavior. In leech, some PMNs rhythmically oscillate in both swimming and crawling but with different frequencies; some fire in crawling but are silent in swimming [29]. In marine mollusk Tritonia Diomedea, the dorsal swim interneurons also make direct connections with the crawling-related cilia MNs and can induce crawling [30].…”

Division of developmental phases of freshwater leech Whitmania pigra and key genes related to neurogenesis revealed by whole genome and transcriptome analysis

“…Identifiable by electrical characteristics and function, each neuron plays a specific and unique role [ 12 ]. The differentiation of these nerve cells started at stage 6a in leech embryos [ 13 ], but the genes involved in the leech neural differentiation are not clear. Thus, elucidating the molecular mechanism of embryonic development in W. pigra could potentiate W. pigra as a model for developmental biology.…”

Genome and transcriptome of freshwater leech Whitmania pigra reveal key genes related to morphogenesis, signal pathways and neurogenesis during embryonic development

“…Identifiable by electrical characteristics and function, each neuron plays a specific and unique role (Nicholls and Baylor 1968). The differentiation of these nerve cells started at stage 6a in leech embryos (Kuo et al 2020), but the genes involved in the leech neural differentiation are not clear. Thus, elucidating the molecular mechanism of embryonic development has been a research hotspot in the scientific community.…”