Waterbird-Mediated Dispersal and Freshwater Biodiversity: General Insights From Bryozoans

Abstract

Freshwater environments are fragmented and heterogeneous in space and time. Long term persistence thus necessitates at least occasional dispersal of aquatic organisms to locate suitable habitats. However, the insubstantial movements of many require zoochory-hitchhiking a ride with more mobile animals. We review evidence for waterbird-mediated zoochory of freshwater bryozoans, a group that provides an excellent model for addressing this issue. The feasibility of long distance transport by waterbirds of bryozoan propagules (statoblasts) is evaluated in relation to statoblast resistance to extreme conditions and waterbird gut retention times, flight durations and distances. We highlight genetic evidence for colonization following waterbird-mediated transport. The consequences of zoochory for biodiversity are manifold. Taxa that release statoblasts show lower levels of genetic differentiation, genetic divergence and haplotype diversity than those whose statoblasts are retained in situ (hence less available for zoochory). Zoochory may also disseminate pathogens and parasites when infected host stages are transported. Such co-dispersal may explain some disease distributions and is supported by viability of infected statoblasts. Zoochory can also be expected to influence local and regional population and community dynamics, food web structure and stability, and organismal distributions, and abundances. Finally, zoochory may influence host-parasite coevolution and disease dynamics across the landscape with the benefits to parasites depending on their life history (e.g., simple vs. complex life cycles, generalists vs. specialists). Our synthesis highlights the complex ecological and evolutionary impacts of zoochory of freshwater organisms and raises questions for future research.

To remain or leave: Dispersal variation and its genetic consequences in benthic freshwater invertebrates

“…The above arguments suggest that general lack of conformation to Hardy-Weinberg equilibrium in both species may be explained by founder effects and selection in F. sultana and bottlenecks in C. mucedo populations. Further independent evidence in support of the contrasting patterns of genetic variation in these two species is obtained from analyses of mtDNA variation in populations from Switzerland and the UK (Okamura et al, 2019). Analysis of molecular variance (AMOVA) demonstrated genetic divergence between populations from the two countries for F. sultana but not for C. mucedo.…”

“…For example, statoblasts may be disseminated by animal vectors that either require hydrological connectivity (e.g., fish) to reach distant sites or that may be prone to follow water courses (e.g., humans, other mammals or birds). Notably C. mucedo statoblasts are often observed in digestive tracts of fish and waterbirds and in waterbird feces, and they have been shown to hatch after passage through vertebrate digestive tracts (Okamura et al, 2019). Rafting of colonies could also contribute to gene flow.…”

“…In addition, band recovery data from waterbirds explain a significant proportion of variation in both genetic distance and gene flow among C. mucedo populations (Figuerola, Green, & Michot, ). The presence of statoblasts in fish guts (Mouronval et al, ) suggests that movements of fish or piscivorous birds might also effect dispersal (Okamura, Hartikainen, & Trew, ). However, buoyancy of statoblasts would also be expected to confer dispersal along hydrologically connected systems.…”

“…Abd‐Elfattah, El‐Matbouli, and Kumar () showed that a proportion of F. sultana statoblasts ingested by carp (but not brown trout) were viable and thus provide some proof‐of‐concept that fish may effect dispersal. However, no records of F. sultana statoblasts in wild caught birds or fish were encountered during preparation of a recent review by one of us (Okamura et al, ). This suggests that F. sultana statoblasts are relatively rarely ingested, perhaps reflecting their adherent nature and lack of spines.…”

Diversidade e revisão taxonômica da família Beaniidae (Bryozoa, Cheilostomata)

“…1.1 C-D) (MCKINNEY & JACKSON, 1991;WAESHANBACK et al, 2012). A Classe Phylactolaemata abriga aproximadamente 100 espécies não calcificadas, sendo caracterizada por apresentar lofóforo em forma de ferradura e se reproduzir assexuadamente pela propagação de estatoblastos (MASSARD & GEIMER, 2008;OKAMURA et al, 2019). Stenolaemata, por sua vez, incluí cerca de 10% (~550) das espécies marinhas viventes, com colônia calcificada e autozooides de forma cilíndrica e polipídio envolto em um saco membranoso (COOK et al, 2018); além disso, a classe é a única que apresenta casos de desenvolvimento embrionário múltiplo (=poliembrionia) em câmaras incubadoras (JENKINS et al, 2017).…”