Proposed Paper: Post-glacial climate velocity as a predictor of genetic diversity and demographic history in the marine tropics - May 24, 2015

Lead: Elizabeth Sbrocco - elizabeth.sbrocco@gmail.com

Those interested in co-authorship should email me with an indication of how you hope to contribute to the paper. I am particularly interested in help from those that can contribute to coalescent analyses of demographic changes over time.

Background and Questions

Species are expected to respond to climatic shifts in one of three ways: disperse to remain within their optimal environment, adapt to novel conditions as they arise, or suffer the fate of local extinction. A species' individual response will depend in part on its ability to disperse, but also on its degree of local adaptation, its adaptive capacity, and the magnitude and direction (a.k.a. the "velocity") of change in its surrounding environment. In the tropical Indo-Pacific, two-thirds of reef-building corals occupy climatic conditions with no analog during the last glacial maximum, and while overall species richness is higher under these novel climatic combinations, richness declines with increasing post-glacial climate velocity (Sbrocco in prep). In other words, reef-building corals are more sensitive to the rate of change in climate than its magnitude of change.

Here I propose to build on my previous work by asking whether genetic diversity and the demographic history of marine organisms inhabiting Indo-Pacific coral reefs are impacted by post-glacial climate velocity. The prediction is that populations inhabiting less stable, more rapidly changing reefs will possess lower genetic diversity, smaller effective population sizes, and/or recent changes in population size, whereas more stable reefs should possess higher genetic diversity and large/stable effective population sizes. I also predict that less vagile species will be more sensitive to the velocity of change due to dispersal limitations.

By exploring how populations have responded to the velocity of climate change over geological time, we can make educated hypotheses regarding the fate of reef organisms over the next century of change. These results could help guide management decisions for populations on high velocity reefs.

Proposed Methods

Species: I will choose a dozen or so representative species from the DIPnet database that have good genetic data sampled across their described ranges AND vary with respect to pelagic larval duration.

Measuring genetic diversity and demographic history: The working group is currently developing novel measures of genetic diversity in order to gain more signal out of species with unique haplotypes for nearly every individual (i.e., many fish sequenced for the mitochondrial control region). I will likely adopt whatever measure of diversity that is used by the group. Demographic history will be inferred using coalescent methods. I COULD USE HELP WITH THE COALESCENT ANALYSES - PLEASE CONTACT ME IF YOU THINK YOU COULD CONTRIBUTE IN THIS WAY.

Defining "climate velocity:" Velocity will be estimated in two ways which vary in their assumptions about local adaptation.

1. A metric-based approach. Here I will use the climate velocity metrics developed for my coral study referenced above to predict genetic diversity and demographic history for each species. For each pixel on a map, the velocity metrics indicate a) the difference between climatic conditions today and the most similar climatic conditions during the LGM (degrees/21ky), b) the geographic distance from each pixel today to the most similar climatic conditions during the LGM (km/21ky), and c) a linear combination of these two metrics (km.deg/21ky). This method assume that populations are locally adapted to the climatic conditions found in their present location.
2. A niche modeling approach. I will develop species distribution models to estimate each species' predicted distribution today and during the LGM. The geographic distance between each population and the closest pixel predicted to be suitable during the LGM will be used as a measure of climate velocity (km/21ky). This method assumes there is no local adaptation across the range of the species, such that climatic conditions that are suitable for one population are equally suitable for all other populations.

Analyses: For both approaches, I will use regression-based analyses, controlling for spatial autocorrelation, to determine the relationship between climate velocity and estimates of genetic diversity/demographic history.