Natural Laboratory for Evolution: Biodiversity Evolution in the Ogasawara Islands

Much like the Galapagos Islands, renowned as evolutionary hubs, the Ogasawara Islands boast a unique ecosystem teeming with endemic species. This distinct biodiversity emerged due to evolutionary processes in an environment secluded from the mainland. Our research prominently features land mollusks, which have experienced significant diversification. We are delving into various facets of evolution, including the process of speciation, mechanisms preserving species diversity, environmental adaptation pathways, and the roles of hybridization in spawning new traits. Moreover, we are dedicated to conservation efforts, aiming to protect this unparalleled ecosystem from threats like invasive foreign species. （Davison & Chiba 2006, 2008; Chiba 2005, 2007, 2010; Wada et al 2013; Chiba & Cowie 2016; Uchida et al 2016; Shinobe et al 2017; Hirano et al 2018; Saito et al 2022; Ito et al 2023）

 

 

Elucidating the Genetic Mechanisms Governing Body Asymmetry in Bivalves

While body asymmetry is typically concealed externally, mollusks are an exception, visibly showcasing left-right asymmetry. Intriguingly, certain species manifest both right- and left-handed asymmetries within the same population due to mutations. Probing the genetic mechanisms behind such mirror polymorphisms could offer insights into body asymmetry determination. In collaboration with researchers from the University of Nottingham, we identified that mutations in the Ldia2 gene, encoding formins that regulate the cytoskeleton, dictate the reversal of shell coiling direction in freshwater bamboo mussels. Our work also delves into the mechanisms determining shell coiling direction, implicating alternate expressions of this and other genes (Davison et al. 2016, 2020; Richards et al. 2017).

 

 

Behavioral, Ecological, and Genetic Studies of Reptiles, Amphibians, and Birds

We examine the evolutionary impact of environmental factors and interspecific relationships on gecko behavior, their environmental adaptability, mechanisms, and genetic differentiation. Our findings suggest that Japanese geckos, originating from China, underwent genetic shifts while migrating eastward. Our research also encompasses avian wing function and morphology, studying the influence birds have on organism migration and the behavior, structure, and interspecific dynamics of shorebirds and plovers (Wada et al. 2012; Chiba M et al. 2022; Saito et al. 2023; Tatani et al. 2023).

 

 

Evolution and Genomics of Mollusks

Our approach primarily uses genome-wide SNP analysis (Rad-seq) in mollusks to unravel biological and environmental catalysts for speciation, investigate population genetic structures, and demystify the processes behind genetic diversity formation. Furthermore, we study the genetic underpinnings of color polymorphisms, coiling direction, and reproductive behavior traits via genome analysis (Miura et al. 2018, 2020; Yamasaki et al. 2022; Hirano et al. 2022, 2023; Sano et al. 2022; Kagawa et al. 2023).

 

 

Evolutionary Impacts of Sexual Conflict on Reproductive Behavior

Certain hermaphroditic land snail groups engage in perilous behaviors utilizing unique traits, notably impaling their mates with a "love arrow" organ during mating. We're exploring the hypothesis that the co-evolution of male and female characteristics, in a bid for reproductive success, spearheaded the development of these traits and behaviors.（Koene & Chiba 2006; Kimura & Chiba 2015; Kimura et al 2016; Shibuya et al 2022）

 

 

Evolution of Altruistic Behavior in Sub-Social Insects

Certain insect species that grow during their larval stage on decaying wood demonstrate cooperative nurturing of their offspring. This care is provided not just by the parents but by the group at large. Such altruistic behaviors, including feeding offspring unrelated to them, are observed. Our research delves into the evolutionary mechanisms behind this collective care, investigating whether kinship plays a role in food provision levels (Mori & Chiba 2009).

 

 

Speciation Models in Competition-Neutral Environments

The prevailing belief posits that inter-individual competition is crucial for species formation and phenotype evolution. However, is competition truly essential for the emergence of new traits? Mathematical models have indicated that speciation and niche differentiation can arise even in near competition-neutral scenarios, particularly when reproductive disruptions result from misidentifications during mating (Konuma & Chiba 2007). Computer simulations using individual-based models further support that speciation can manifest in such neutral populations. Moreover, the resulting speciation patterns align closely with those seen in competition-driven speciation, like adaptive dispersal (Suzuki & China 2016).

 

 

Evolutionary Reproducibility

A longstanding debate centers on whether a lineage, under identical conditions, would consistently arrive at the same evolutionary outcomes. Over time and across regions, organisms with analogous specialized traits may emerge independently within distinct lineages, subsequently facing similar extinction patterns. Mathematical models have mapped this pattern — a one-directional shift from generalist to specialist, leading to heightened extinction risks (Chiba 1998). Yet, computer-simulated analyses suggest that evolution, in the presence of intricate inter-individual interactions, neither consistently maintains a direction nor is reproducible based on conditions. Under such circumstances, a specific phenotype might evolve just once in extensive evolutionary timelines (Nonoyama & Chiba 2019).

 

 

Ecology of Extinction

Our research probes whether extinction patterns, across populations and lineages, showcase distinct selectivity based on causative factors or if there are universal traits predisposing them to extinction. In studies focusing on land mussels, we've ascertained that varied causative factors lead to different extinction selectivity. Such selectivity makes communities more susceptible to disruptions, especially when extinctions stem from multifactorial causes. Furthermore, our findings suggest that certain island species were predisposed to disruptions even before human activities began, leading to their extinction early into human colonization (Chiba et al 2009; Chiba & Roy 2011; Chiba 2023).

 

 

Invasive Species Control via Advanced Technologies

Traditional control measures against invasive species — encompassing chemical treatments, biological countermeasures, manual extermination, and surveillance — are often hindered by cost and environmental concerns, posing challenges to control initiatives. To address these limitations, we're pioneering control techniques using RNA interference targeting invasive species such as the alien borers and carnivorous land snails plaguing the Ogasawara and Ryukyu Islands. We're also probing the genetic underpinnings of these species' physiological functions via genome analysis, aiming for gene drive-based control. In parallel, we've crafted an automated surveillance system for these invasive species, amalgamating AI with drone-based aerial photography, enhancing monitoring efficiency while minimizing costs (Aota et al 2021).