Kayoko Fukumori

Male ornamentation and its condition-dependence in a paternal mouthbrooding cardinalfish with extraordinary sex roles

Cardinalfishes, in which males alone provide mouthbrooding, are likely candidates for sex-role reversal because of a higher potential reproductive rate for females than for males. In the gregarious cardinalfish, Apogon notatus, females establish breeding territories to form pairs prior to the breeding season. Within breeding pairs, females are more active in courtship and in attacks against conspecific intruders. Sex roles thus seem to be behaviorally reversed. The operational sex ratio is, however, male-biased because females suffer higher mortality than males and consequently males predominate in number in the adult population, leading to the prediction that males would be sexually selected. In the present study, morphological measurements showed that males had a protrudent lower lip that was expressed markedly during the breeding season. Field observation revealed that males with a longer and wider lip were preferentially accepted as a mating partner by territorial females. The male lip size positively correlated with their somatic condition, suggesting that the ornamental lip has evolved through indicator mechanisms of sexual selection. By contrast, females had longer fins than males, but these sexual dimorphisms were less pronounced and most of them were seasonally constant. These results support the prediction that sexual selection acts on males in this fish.

Disturbance‐mediated colonization–extinction dynamics in experimental protist metacommunities

Colonization-extinction dynamics and species sorting among habitats deter- mine the distribution of species within metacommunities. Theory suggests that disturbances reduce the importance of species sorting and enhance spatial patterning and stochastic effects, however this has not yet been experimentally shown. We examined how extinctions in a heterogeneous landscape of patches affects the influence of environmental, spatial, and stochastic factors on community composition in a simple two-species, two-habitat, protist metacommunity where each species dominates in a different habitat type. We imposed four different levels of random extinctions on local patches and monitored changes in the metacommunity through time. We found that near-steady state patterns of community variability developed relatively rapidly (within nine colonization-extinction cycles) and that increased extinction rate produced altered patterns of community regulation by reducing environmental control and increasing spatial and stochastic effects. Our results indicate a possible explanation for the combination of environmental, spatial and stochastic effects observed in natural metacommunities.

Female territoriality in a paternal mouthbrooding cardinalfish to avoid predation against spawned eggs

Generally, paternal mouthbrooding cardinalfishes are characteristic of sex-role-reversed animals: females have a higher potential reproductive rate and are more active in mating competition than males, and the operational sex ratio (OSR) is female-biased. However, one species of cardinalfish, Apogon notatus (Houttuyn, 1782), shows unusual sex roles: females alone defend their breeding territories to form pairs, even though the OSR is male-biased. This is inconsistent with the general rule that breeding territoriality is shown by the more abundant sex. We examined the function of female breeding territory in this fish using field observations. Prior to the breeding season, large females established their territories earlier than small females. Earlier settlers occupied deeper areas with larger boulders where conspecifics were less likely to aggregate. As the level of conspecific aggregation increased, spawning females suffered from frequent intraspecific interference and subsequent egg predation, leading t...

Predators regulate prey species sorting and spatial distribution in microbial landscapes

The role of predation in determining the metacommunity assembly model of prey communities is understudied relative to that of interspecific competition among prey. Previous work on metacommunity dynamics of competing species has shown that sorting by habitat patch type and spatial patterning can be affected by disturbances. Microcosms offer a useful model system to test the effect of multi-trophic interactions and disturbance on metacommunity dynamics. Here, we investigated the potential role of predators in enhancing or disrupting sorting and spatial pattern among prey in experimental landscapes. We exposed multi-trophic protist microcosm landscapes with one predator, two competing prey, two patch resource types, and localized dispersal to three disturbance regimes (none, low, and high). Then, we used variation partitioning and spatial clustering analysis to analyse the results. In contrast with previous experiments that did not manipulate predators, we found that patch type did not structure prey communities very well. Instead, we found that it was the distribution of the predator that most strongly predicted the composition of the prey community. The predator impacted species sorting by (1) preferentially consuming one prey, thereby acting as a strong local environmental driver, and by (2) indirectly magnifying the impact of patch food resources on the less preferred prey. The predator also enhanced spatial signal in the prey community because of its limited dispersal. Our results indicate that predators can strongly influence prey species sorting and spatial patterning in metacommunities in ways that would otherwise be attributed to stochastic effects, such as dispersal limitation or demographic drift. Therefore, whenever possible, predators should be explicitly included as separate explanatory factors in variation partitioning analyses.

Food web properties of the recently constructed, deep subtropical Fei-Tsui Reservoir in comparison with the ancient Lake Biwa

Using carbon and nitrogen stable isotope analysis, we characterised food web properties of the deep subtropical Fei-Tsui Reservoir (FTR), which was recently altered from a lotic to a lentic system after dam construction. In the littoral zone, zoobenthos showed strong reliance (83.9%) on benthic algal production. Zoobenthos were never found in the profundal zone because of anoxia. Zooplankton depleted 13C more than that of particulate organic matter as their putative food source, suggesting a contribution of methane-derived carbon to pelagic food webs. Excluding juveniles, non-native and fluvial species, adult fish showed strong reliance (on average 80.9%) on benthic production, weakly coupled with pelagic food webs. These results contrast low benthic production reliance (on average 27.4%) for a fish community in Lake Biwa, which is also classified as a subtropical lake. Both lakes are characterised by deep pelagic waters but quite different in their geological ages, suggesting that the aquatic communities in the FTR have fluvial origins, and their lacustrine history was too short for them to adapt to newly emerged deep pelagic habitat. Our isotope data are useful as a reference of newly established lentic food webs to monitor ongoing ecological and evolutionary dynamics as a result of anthropogenic disturbances.

Origin and Diversification of Freshwater Fishes in Lake Biwa

Lake Biwa is the largest and oldest lake in Japan. It harbors more than a thousand animal and plant species, including 67 indigenous freshwater fish species/subspecies with 16 endemic or semi-endemic forms. Paleogeographical and paleontological studies have revealed that the location and environment of the lake have changed during its history of more than four million years. The current Lake Biwa, with its unique environments, was established 0.4 million years ago. Endemic fishes in Lake Biwa are traditionally divided into old “relict species” and new “species that evolved in the lake,” the latter being assumed to have evolved through ecological adaptations to the present lake environment. However, recent molecular phylogenetic/population genetic analyses have revealed that many of the “species that evolved in the lake” have origins that are older than the present Lake Biwa, while other species likely evolved in the present environment through ecological adaptation. On the other hand, many fish populations that inhabit Lake Biwa, irrespective of their origin, show similar patterns involving recent population expansions that occurred several tens of thousands of years ago. Extensive community level analyses of “lacustrine syndromes” that are found in Lake Biwa are necessary based on morphology, physiology, phylogenetics, population genetics, and also new “omics” approaches.

Predator Diversity Changes the World: From Gene to Ecosystem

Trophic polymorphism, defined as the state in which two or more clearly different feeding functional traits exist within the same population of a species, is general in fishes. In aquatic ecosystems, the fishes often have strong impacts on prey communities as keystone predators, so that phenotypic divergence of their feeding traits can alter biotic and abiotic attributes of environments through changes in the form of trophic interactions. The predator-induced environmental alterations may, in turn, drive evolutionary changes in adaptive traits of themselves as well as of other members in the communities. This process, in which ecology and evolution reciprocally interplay over contemporary time-scales, is termed “eco-evolutionary feedback.” In this chapter, we review how and when trophic polymorphism has been generated in fish populations and then discuss what consequences it has in ecological and evolutionary aspect. Special references are made to the case in the ancient Lake Biwa, which has a geological history long enough for divergent fish populations to come to ecological speciation and thus provides a good opportunity to understand how such an evolutionary process diversifies biological communities and consequently ecosystem properties in lakes.

Biodiversity Researches on Microbial Loop in Aquatic Systems

The food linkage between heterotrophic bacteria and protists is so-called “microbial loop,” functioning as important matter cycling in pelagic food webs. Biomass of heterotrophic bacteria sometimes predominates total heterotrophic biomass in lakes, and organic matter transfer started from heterotrophic bacteria has been intensively studied by numerous researchers all over the world. The roles of planktonic protists, such as heterotrophic nanoflagellates and ciliates, in microbial loop are to consume bacteria that are too small to serve directly as major prey items for most zooplankters, and to be themselves utilized by the zooplankton. There is a consensus that food linkages between bacteria and protists are substantial in many lakes. In addition, bacterial loss due to viral lysis has also been paid great attention by many researchers since the late 1990. The present review provides the overview on the trend and future stage of microbial loop researches in freshwater systems, with special reference to culture-independent molecular techniques such as PCR cloning and sequencing, fluorescently in situ hybridization or denaturing gradient gel electrophoresis for phylogenetic analyses on microbial communities. A review on ecology and biodiversity researches on microbial loop in Lake Biwa is also provided.

A Dynamic Resilience Perspective Toward Integrated Ecosystem Management: Biodiversity, Landscape, and Climate

Ecosystems often show sudden and drastic shifts in their states following relatively small environmental changes, yet the environmental restoration does not necessarily easily recover the original state. The resilience theory has played a pivotal role in ecosystem management by providing a theoretical basis for such abrupt and irreversible phase transitions (i.e., regime shifts). However, a major concern remains that the existing theory considers ecosystem responses along only a single disturbance axis (e.g., eutrophication), despite the fact that natural ecosystems are subject to multiple anthropogenic disturbances. In this chapter, I introduce ontogenetic niche shifts (i.e., changes in resource use or predation vulnerability during individual growth) as a possible common mechanism of regime shifts. Based on this framework, I show how additional factors not accounted for the basic resilience theory (e.g., species extinction and invasion, habitat loss and fragmentation, and phenological shifts) may affect whether or where regime shifts occur along environmental gradients. I conclude that these results taken together illustrate the importance of interdisciplinary research integrating biodiversity conservation, landscape protection, and climate change adaptation for more effective management of lake ecosystems.