At this stage of the Great Acceleration of the Anthropocene, humanity is experiencing the global issues of worsening climate change impacts, devastating damage from more frequent and severe natural disasters and the COVID-19 pandemic, all of which are attributable to ecosystem degradation and biodiversity loss. The global community recognises that these issues pose severe societal and economic risks. “Nature-based solutions” have been posited as a means to address these threats. Nature-based solutions utilise natural terrestrial ecosystem functions to provide environmental, social and economic benefits at low cost. The growing social demand for nature-based solutions constitutes an opportunity for the field of ecology to expand beyond the conventional focus on biodiversity and conservation and shift to presenting biodiversity and ecosystem functions as the basis of human well-being and social sustainability. We sought to identify a trajectory for ecological research that is aimed at contributing to the effective implementation of nature-based solutions. First, we summarise current social needs related to terrestrial ecosystem utilisation. Next, we provide an overview of existing literature and knowledge regarding biodiversity and terrestrial ecosystem function, which are critical to nature-based solutions. Finally, we identify outstanding ecological hurdles to the implementation of these strategies and propose a way forward based on our findings. We explain that any basic presentation of ecological processes requires addressing the impacts of climate change and the interrelatedness of biodiversity, climate and social systems. Enhanced ecological process models are critical for linking biodiversity and ecosystems with climate and social systems. It is crucial to establish a framework that embeds monitoring systems, data infrastructure and delivery systems within society to mobilise terrestrial ecosystem and biodiversity data and results. Furthermore, the implementation of nature-based solutions must include acknowledging trade-offs in objectives and transdisciplinary research with other fields and stakeholders with the shared goal of transformative change. Ecological research must demonstrate more clearly how terrestrial biodiversity and ecosystems are linked to human health and well-being, as well as how they are affected by production and consumption systems. In the age of climate change, the knowledge and tools of the ecologist form the foundation of nature-based solutions and provide an indispensable theoretical basis for this approach.

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Insects display a wide variety of sexual dimorphism including size, ornamentation and colouration. For example, in species for which males fight one another for access to mates and fitness, males have enlarged weapon traits for fighting. In species for which males exhibit colorful ornamentation, more colourful males are preferred by females. In addition, insects often show sex differences in leg morphology, with males possessing longer or thicker developed legs. These structures are notable because of the exaggerated length or thickness. The developed legs of males are thought to function in male-male competition and copulation with females. Legs are important for reproduction not only in males but also in females, who often use their legs to resist sexual harassment by males. Thus, the legs of insects play a key role in reproduction regardless of sex. Here, we summarise our research and discuss the influence of legs on reproduction in insects.

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Males of various species of Scarabaeoidea with horns or enlarged mandibles also have elongated forelegs. The co-occurrence of these male traits raises the question of whether the forelegs and mandibles/horns are functionally related and thus examples of correlated evolution. Few studies have examined in detail how these multiple weapons are used in contests. In this paper, I explain the function of elongated forelegs and horns in male?male competition of the Taiwanese flower beetle, Dicronocephalus wallichii bourgoini (Coleoptera: Scarabaeidae: Cetoniinae). Individuals of this species aggregate on bamboo shoots, where they mate and injure the shoots to feed on sap. Males mount the females after copulation for several hours. The sex ratio at feeding sites is male biased, and competition between the mate-guarding (i.e., owners) and unpaired males (i.e., intruders) frequently occurs. Analyses of the sequence of competition indicated that an owner would touch an intruder's body with its forelegs and then intensely move the forelegs, probably to assess the body size or fighting ability of the opponent. In escalated contests, both opponents tried to drag the other away from the female or substrate mainly using horns. This suggests that their multiple weapons are specialized for specific phases of contests. Males with larger weapons (or bodies) were more successful in defending ownership of their mates. Analyses of horn and foreleg allometry also suggested that these traits are products of sexual selection. Furthermore, I tested whether elongated forelegs impede the maximum sprint speed on bamboo branches. There was no negative relationship between relative foreleg length and sprint speed. Additionally, males with longer forelegs were found to have longer midlegs and hindlegs, independent of body size. Thus, elongated midlegs and hindlegs in males may enhance balance, stabilize running on bamboo branches, and compensate for the locomotor costs of possessing enlarged forelegs.

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Sexually exaggerated traits are widespread among insects, and exaggerated parts of the body vary among species. The body parts and exaggeration levels are associated with the style and intensity of fights for access to resources, such as food and mates, as well as territories that contain these resources. Likewise, the characterization of sexually exaggerated traits is associated with whether the traits are used as ornaments. Therefore, to clarify how sexually exaggerated traits have evolved and been maintained, it is necessary to deepen our understanding of the natural history of each species. Several researchers and I have studied the morphology and behavior of Drosophila prolongata (Diptera: Drosophilidae). Males of this species have exaggerated forelegs, which they use for intrasexual aggression as well as courtship for females. However, little is known about the biological characteristics of D. prolongata in the wild. The use of legs in intrasexual competition has rarely been reported in other dipterans. Elucidating the ecological factors that have favored the evolution of exaggerated forelegs in D. prolongata males may help clarify why the legs are not used as weapons as in other flies. In this paper, I discuss the evolutionary mechanisms of sexually exaggerated legs in insects with regard to their feeding habits and oviposition sites. I also introduce inter- and intraspecific variation in morphological and behavioral traits of D. prolongata and outline the relationship between aggressiveness and life-history traits.

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Indiscriminate courtship and interspecific mating can lead to reproductive interference. Callosobruchus chinensis males cause asymmetric reproductive interference in C. maculatus females through interspecific copulation, and its intensity depends on the magnitude of sexual selection within a population. Female C. maculatus kick their mates to reduce their mating cost, especially copulatory tract wounds. Therefore, we hypothesized that the intensity of reproductive interference differs among geographic strains of C. maculatus in which female kicking reduces the intensity of reproductive interference. To test this hypothesis, we measured the hind leg morphometrics, interspecific copulation behavior, and lifetime reproductive success with/without heterospecific males in females of two geographic C. maculatus strains. Morphometrically, body size differed between the strains and hind legs were longer with increased body size. The larger strain tended to kick during mating; a high frequency of kicking suppressed the expected ejaculation by C. chinensis males. We also found that the lifetime reproductive success of C. maculatus females varied significantly by both strain and heterospecific male treatment and that the larger strain did not decrease its fitness with heterospecific males. These results indicate that interspecific mating between C. chinensis males and C. maculatus females depends on female body size, and the copulation duration affects the intensity of reproductive interference.

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Movement has a profound effect on male reproduction. Males with higher levels of moving activity are predicted to have higher mating success, because they are encounter more females. Males with lower migratory activity and lower encounter rates with females are predicted to invest more in maximizing post-mating fertilization success than in increasing mating success. In insects, the legs are important appendages not only for movement, but also for mating, and sexual dimorphism in leg morphology has been observed in various species. In male legs, the morphology advantageous for movement may also be disadvantageous for grasping a female during mating, suggesting that male legs are formed via various selection pressures. Males with lower moving activity, which are likely to invest more in increasing fertilization success, are expected to exhibit different leg morphologies from males with higher moving activity. In this study, we investigated the response of reproductive traits and leg morphology to artificial selection for walking activity in the red flour beetle Tribolium castaneum Herbst. The results indicated that males from strains selected for lower moving activity had significantly longer legs than those from strains selected for higher moving activity. The former males may use their long legs to grasp females, thus prolonging mating. In addition, males selected for lower moving activity exhibited greater fertilization success, suggesting that long legs are important for male reproduction. Based on the results of our studies, I discuss the evolution of sexual size dimorphism of legs, and interspecific variation in the degree thereof.

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[in Japanese]

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[in Japanese]

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[in Japanese]

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