Posts

Posted on

Cophylogeny and specificity between cryptic coral species (Pocillopora spp.) at Mo’orea and their symbionts (Symbiodiniaceae)

In press, Molecular Ecology https://doi.org/10.1111/mec.16654

Erika C. Johnston, Ross Cunning, Scott C. Burgess

Abstract:

The congruence between phylogenies of tightly associated groups of organisms (cophylogeny) reflects evolutionary links between ecologically important interactions. However, despite being a classic example of an obligate symbiosis, tests of cophylogeny between scleractinian corals and their photosynthetic algal symbionts have been hampered in the past because both corals and algae contain genetically unresolved and morphologically cryptic species. Here, we studied co-occurring, cryptic Pocillopora species from Mo’orea, French Polynesia, that differ in their relative abundance across depth. We constructed new phylogenies of the host Pocillopora (using complete mitochondrial genomes, genomic loci, and thousands of single nucleotide polymorphisms) and their Symbiodiniaceae symbionts (using ITS2 and psbAncr markers) and tested for cophylogeny. The analysis supported the presence of five Pocillopora species on the fore-reef at Mo’orea that mostly hosted either Cladocopium latusorum or C. pacificum. Only Pocillopora species hosting C. latusorum also hosted taxa from Symbiodinium and Durusdinium. In general, the Cladocopium phylogeny mirrored the Pocillopora phylogeny. Within Cladocopium species, lineages also differed in their associations with Pocillopora haplotypes, except those showing evidence of nuclear introgression, and with depth in the two most common Pocillopora species. We also found evidence for a new Pocillopora species (haplotype 10), that has so far only been sampled from French Polynesia, that warrants formal identification. The linked phylogenies of these Pocillopora and Cladocopium species and lineages suggest that symbiont speciation is driven by niche diversification in the host, but there is still evidence for symbiont flexibility in some cases.

Posted on

Dispersal, kin aggregation, and the fitness consequences of not spreading sibling larvae

Scott C. Burgess, Jackson Powell, Marília Bueno.

In press, Ecology https://doi.org/10.1002/ecy.3858

Abstract: Dispersal has far-reaching implications for individuals, populations, and communities, especially in sessile organisms. Escaping competition with conspecifics and with kin are theorized to be key factors leading to dispersal as an adaptation. However, manipulative approaches in systems where adults are sessile but offspring have behaviors is required for a more complete understanding of how competition affects dispersal. Here, we integrate a series of experiments to study how dispersal affects the density and relatedness of neighbors, and how the density and relatedness of neighbors in turn affects fitness. In a marine bryozoan, we empirically estimated dispersal kernels and found that most larvae settled within ~1 m of the maternal colony, though some could potentially travel at least 10’s of meters. Larvae neither actively preferred or avoided conspecifics or kin at settlement. We experimentally determined the effects of spreading sibling larvae by manipulating the density and relatedness of settlers and measuring components of fitness in the field. We found that settler density reduced maternal fitness when settler neighbors were siblings compared to when neighbors were unrelated or absent. Genetic markers also identified very few half sibs (and no full sibs) in adults from the natural population, and rarely close enough to directly interact. In this system, dispersal occurs over short distances (meters) yet, in contrast to expectations, there appears to be limited kinship between adult neighbors. Our results suggest that the limited dispersal increases early offspring mortality when siblings settle next to each other, rather than next to unrelated conspecifics, potentially reducing kinship in adult populations. High offspring production and multiple paternity could further dilute kinship at settlement and reduce selection for dispersal beyond the scale of 10’s of meters.

Posted on

Cophylogeny and specificity between cryptic coral species (Pocillopora spp.) at Mo’orea and their symbionts (Symbiodiniaceae)

Erika C. Johnston, Ross Cunning, Scott C. Burgess

bioRxiv 2022.03.02.482706

https://doi.org/10.1101/2022.03.02.482706

Abstract: The congruence between phylogenies of tightly associated groups of organisms (cophylogeny) reflects evolutionary links between ecologically important interactions. However, despite being a classic example of an obligate symbiosis, tests of cophylogeny between scleractinian corals and their photosynthetic algal symbionts have been hampered in the past because both corals and algae contain genetically unresolved and morphologically cryptic species. Here, we studied co-occurring, cryptic Pocillopora species from Mo’orea, French Polynesia, that differ in their relative abundance across depth. We constructed new phylogenies of the host Pocillopora (using genomic loci, complete mitochondrial genomes, and thousands of single nucleotide polymorphisms) and their Symbiodiniaceae symbionts (using ITS2 and psbAncr markers) and tested for cophylogeny. The analysis supported the presence of five Pocillopora species on the fore-reef at Mo’orea that mostly hosted either Cladocopium latusorum or C. pacificum. Only Pocillopora species hosting C. latusorum, and that have similar relative abundances across depths, also hosted taxa from Symbiodinium and Durusdinium. In general, the Cladocopium phylogeny mirrored the Pocillopora phylogeny. Within Cladocopium species, lineages also differed in their associations with Pocillopora haplotypes, except those showing evidence of nuclear introgression, and with depth in the two most common Pocillopora species. We also found evidence for a new Pocillopora species (haplotype 10), that has so far only been sampled from French Polynesia, that warrants formal identification. The linked phylogenies of these Pocillopora and Cladocopium species and lineages suggest that symbiont speciation is driven by niche diversification in the host, but there is still evidence for symbiont flexibility in rare cases.

Posted on

Individual variation in marine larval-fish swimming speed and the emergence of dispersal kernels

Scott Burgess, Michael Bode, Jeffrey Leis, Luciano Mason (2021) Individual variation in marine larval-fish swimming speed and the emergence of dispersal kernels. Oikos https://doi.org/10.1111/oik.08896

Abstract: Dispersal emerges as a consequence of how an individual’s phenotype interacts with the environment. Not all dispersing individuals have the same phenotype, and variation among individuals can generate complex variation in the distribution of dispersal distances and directions. While active locomotion performance is an obvious candidate for a dispersal phenotype, its effects on dispersal are difficult to measure or predict, especially in small organisms dispersing in wind or currents. Therefore, we analyzed the effects of larval swimming on dispersal and settlement of coral-reef fish larvae using a high-resolution biophysical model. The model is, to date, the only biophysical model of marine larval dispersal that has been statistically validated against genetic parentage estimates of larval origin and destination, and incorporates empirically-estimated larval behaviors and their ontogeny. Larval swimming, in combination with depth, orientation and navigation behaviors, actually reduced dispersal distances compared to those of passive larvae. Swimming had no consistent effects on long distance dispersal, but increased the spread of settlement locations. Swimming speed, in contrast, did not consistently affect median dispersal distances, but faster swimming larvae had greater mean and maximum dispersal distances than slower swimming larvae. Finally, faster larval swimming speeds consistently increased the probability of settlement. Our analysis shows how larval swimming differentially affects multiple properties of dispersal kernels. In doing so, it indicates how selection could favor faster larval swimming to increase settlement and local retention, which may actually result in longer dispersal distances as a by-product of larvae trying to locate habitat rather than to disperse greater distances.

Posted on

Fluctuating selection and global change: a synthesis and review on disentangling the roles of climate amplitude, predictability and novelty

Bitter MC, Wong JM, Dam HD, Donelam SC, Kenkel CD, Komoroske LM, Nikols KJ, Rivest EB, Salinas S, Burgess SC, and Lotterhos KE (2021) Fluctuating selection and global change: a synthesis and review on disentangling the roles of climate amplitude, predictability, and novelty. Proceedings of the Royal Society B. https://doi.org/10.1098/rspb.2021.0727 PDF

Abstract: A formidable challenge for global change biologists is to predict how natural populations will respond to the emergence of conditions not observed at present, termed novel climates. Popular approaches to predict population vulnerability are based on the expected degree of novelty relative to the amplitude of historical climate fluctuations experienced by a population. Here, we argue that predictions focused on amplitude may be inaccurate because they ignore the predictability of environmental fluctuations in driving patterns of evolution and responses to climate change. To address this disconnect, we review major findings of evolutionary theory demonstrating the conditions under which phenotypic plasticity is likely to evolve in natural populations, and how plasticity decreases population vulnerability to novel environments. We outline key criteria that experimental studies should aim for to effectively test theoretical predictions, while controlling for the degree of climate novelty. We show that such targeted tests of evolutionary theory are rare, with marine systems being overall underrepresented in this venture despite exhibiting unique opportunities to test theory. We conclude that with more robust experimental designs that manipulate both the amplitude and predictability of fluctuations, while controlling for the degree of novelty, we may better predict population vulnerability to climate change.

Posted on

Response diversity in corals: hidden differences in bleaching mortality among cryptic Pocillopora species

Burgess SC, Johnston EC, Wyatt ASJ, Leichter JJ, Edmunds PJ. (2021) Response diversity in corals: hidden differences in bleaching mortality among cryptic Pocillopora species. Ecology https://doi.org/10.1002/ecy.3324

Abstract:

Variation among functionally similar species in their response to environmental stress buffers ecosystems from changing states. Functionally similar species may often be cryptic species representing evolutionarily distinct genetic lineages that are morphologically indistinguishable. However, the extent to which cryptic species differ in their response to stress, and could therefore provide a source of response diversity, remains unclear because they are often not identified or are assumed to be ecologically equivalent. Here, we uncover differences in the bleaching response between sympatric cryptic species of the common Indo-Pacific coral, Pocillopora. In April 2019, prolonged ocean heating occurred at Moorea, French Polynesia. 72% of pocilloporid colonies bleached after 22 days of severe heating (>8°C-days) at 10 m depth on the north shore fore reef. Colony mortality ranged from 11% to 42% around the island four months after heating subsided. The majority (86%) of pocilloporids that died from bleaching belonged to a single haplotype, despite twelve haplotypes, representing at least five species, being sampled. Mitochondrial (open reading frame) sequence variation was greater between the haplotypes that experienced mortality versus haplotypes that all survived than it was between nominal species that all survived. Colonies >30 cm in diameter were identified as the haplotype experiencing the most mortality, and in 1125 colonies that were not genetically identified, bleaching and mortality increased with colony size. Mortality did not increase with colony size within the haplotype suffering the highest mortality, suggesting that size-dependent bleaching and mortality at the genus level was caused instead by differences among cryptic species. The relative abundance of haplotypes shifted between February and August, driven by declines in the same common haplotype for which mortality was estimated directly, at sites where heat accumulation was greatest, and where larger colony sizes occurred. The identification of morphologically indistinguishable species that differ in their response to thermal stress, but share a similar ecological function in terms of maintaining a coral-dominated state, has important consequences for uncovering response diversity that drives resilience, especially in systems with low or declining functional diversity.

Posted on

Niche differences in co-occurring cryptic coral species (Pocillopora spp.)

Johnston, E.C., Wyatt, A.S.J., Leichter, J.J., Burgess S.C (2021) Niche differences in co-occurring cryptic coral species (Pocillopora spp.). Coral Reefs. https://doi.org/10.1007/s00338-021-02107-9

Abstract:

Cryptic species that are morphologically similar co-occur because either the rate of competitive exclusion is very slow, or because they are not, in fact, ecologically similar. The processes that maintain cryptic local diversity may, therefore, be particularly subtle and difficult to identify. Here, we uncover differences among several cryptic species in their relative abundance across a depth gradient within a dominant and ecologically important genus of hard coral, Pocillopora. From extensive sampling unbiased toward morphological characters, at multiple depths on the fore reef around the island of Mo’orea, French Polynesia, we genetically identified 673 colonies in the Pocillopora species complex. We identified 14 mitochondrial Open Reading Frame haplotypes (mtORFs, a well-studied and informative species marker used for pocilloporids), which included at least six nominal species, and uncovered differences among haplotypes in their relative abundance at 5, 10, and 20 m at four sites around the island. Differences in relative haplotype abundance across depths were greater than differences among sites separated by several kilometers. The four most abundant species are often visibly indistinguishable at the gross colony level, yet they exhibited stark differences in their associations with light irradiance and daily water temperature variance. The pattern of community composition was associated with frequent cooling in deeper versus shallower water more than warmer temperatures in shallow water. Our results indicate that these cryptic species are not all ecologically similar. The differential abundance of Pocillopora cryptic species across depth should promote their coexistence at the reef scale, as well as promote resilience through response diversity.