Friday, 6 November 2020

Evolution News - Two More Examples of Evolution in Progress

Monarch butterflies, Danaus plexippus, are known for their lengthy migrations, but in some cases the insects have spread outside their normal range and settled in non-migrating populations. These non-migrating butterflies consistently have smaller wings (bottom, collected in S. America) than migrators (top, collected in San Francisco).
Two Centuries of Monarch Butterflies Show Evolution of Wing Length - Egghead

A couple more examples of evolution in progress being reported on by biologists who had no intention of refuting Creationism, but did so anyway simply by reporting the facts.

The first example is of the monarch butterfly, Danaus plexippus. These North American butterflies are famous for their prodigious migration flights to a small valley in Mexico where they spend the Winter, then out across North America to their breeding grounds in Spring. Those west of the Rocky Mountains also over-winter in sites in Southern California although some do go to Mexico.

Over the years, small populations have been established on Caribbean and Pacific islands, Hawai'i, Australia and in South America, where, because the Winter climate is milder, they have given up migrating and become sedentary species. These colonies have been founded by windblown vagrants. I have even seen them in Puerto Banús, on the southern coast of Andalusia, Spain, where there is a healthy local population.

By examining museum specimens collected since 1856, researchers noticed that the wings of the migratory populations had grown longer over the last 174 years while those of the sedentary species had tended to shorten. To check that this was not due to environmental factors influencing the development of individuals, the team collected specimens from the sedentary populations in Guam, Puerto Rico and Hawai'i and raised them with migratory monarchs outdoors in Davis, California. This confirmed that the sedentary forms retained their shorter wings even in this new environment while the migrating forms retained their longer wings.

In other words, since 1856, two sets of evolutionary pressures had cause the the species to diverger into long and short-winged forms.

Sadly, the published paper in PNAS is behind an expensive paywall, However the details are explained by an article by Andy Fell, in the UC Davis News magazine, Egghead.

Cue: The Creationist cry, "Yeh! But they're still butterflies!"

The second example is of diverging corals from Kāneʻohe Bay Hawaiʻi. According to research by marine biologists from Hawai‘i Institute of Marine Biology (HIMB), this appears to have been an example of co-evolution between the coral polyps, a symbiont algae and symbiotic micro-organisms.

(A) Yellow and blue-grey Porites coral;
(B) bleached coral adjacent to various colors of coral in Kaneohe Bay.
Genomic data ‘catches corals in the act’ of speciation and adaptation | SOEST

In a news release from the University of Hawai'i's School of Ocean and Earth Science and Technology, Marcie Grabowski explains:
As coral reef ecosystems have rapidly collapsed around the globe over the past few decades, there is widespread concern that corals might not be able to adapt to changing climate conditions, and much of the biodiversity in these ecosystems could be lost before it is studied and understood. Coral reefs are among the most highly biodiverse ecosystems on earth, yet it is not clear what drives speciation and diversification in the ocean, where there are few physical barriers that could separate populations.

The team of researchers used massive amounts of metagenomic sequencing data to try to understand what may be some of the major drivers of adaptation and variation in corals.

“Corals have incredible variation with such a wide range of shapes, sizes, and colors that it’s really hard for even the best trained experts to be able to sort out different species,” said Zac Forsman, lead author of the study and HIMB assistant researcher. “On top of that, some corals lose their algal symbionts, turning stark white or ‘bleached’ and die during marine heatwaves, while a similar looking coral right next to it seems fine. We wanted to try to better understand what might be driving some of this incredible variation that you see on a typical coral reef.”

Forsman and colleagues examined genetic relationships within the coral genus Porites, which forms the foundation and builds many coral reefs around the world. They were able to identify genes from the coral, algal symbionts, and bacteria that were most strongly associated with coral bleaching and other factors such as the shape (morphology) of the coral colony. They found relatively few genes associated with bleaching, but many associated with distance from shore, and colony morphologies that dominate different habitats.
What they discovered is that there is evidence of recent divergence over depth and distance from the shore. Not only have the corals diverged but so have their symbiont algae and microbes. In other words, there has been co-evolution of the complex of interdependent species. Their findings were published recently, open access, in Scientific Reports.


The ‘species’ is a key concept for conservation and evolutionary biology, yet the lines between population and species-level variation are often blurred, especially for corals. The ‘Porites lobata species complex’ consists of branching and mounding corals that form reefs across the Pacific. We used reduced representation meta-genomic sequencing to examine genetic relationships within this species complex and to identify candidate loci associated with colony morphology, cryptic genetic structure, and apparent bleaching susceptibility. We compared existing Porites data with bleached and unbleached colonies of the branching coral P. compressa collected in Kāneʻohe Bay Hawaiʻi during the 2015 coral bleaching event. Loci that mapped to coral, symbiont, and microbial references revealed genetic structure consistent with recent host-symbiont co-evolution. Cryptic genetic clades were resolved that previous work has associated with distance from shore, but no genetic structure was associated with bleaching. We identified many candidate loci associated with morphospecies, including candidate host and symbiont loci with fixed differences between branching and mounding corals. We also found many loci associated with cryptic genetic structure, yet relatively few loci associated with bleaching. Recent host-symbiont co-evolution and rapid diversification suggests that variation and therefore the capacity of these corals to adapt may be underappreciated.

The good news from this finding is that given enough time, corals may be more adaptive to environmental change than was previously thought. The challenge is to buy them enough time.

So, contrary to creationist dogma, here we have two observed instances of evolutionary diversification in progress, in both cases driven by the local environment with no change in the amount of genetic information involved, only a change in its meaning. In the case of the Hawai'ian coral, the evolution has not only been of the coral polyps themselves but also of the symbiotic organisms that live in and on them.

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