18th CENTURY MAPS REVEAL MASSIVE LOSS OF CORAL REEFS IN THE FLORIDA KEYS

- story published by Science

Marine scientists have long lamented the decline of Florida’s vibrant coral reefs. Now, nautical maps drawn just before the American Revolutionary War (similar to the one pictured) are giving scientists a clearer idea of just what has been lost. The maps, created by the British Admiralty between 1773 and 1775, record the location of coral reefs—which can be a deadly navigational hazard—along the Florida Keys in southern Florida. Scientists compared the maps to modern charts, finding that more than half of the historical reefs have been replaced by seagrass beds or bare sea floor.

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GECKOS EVOLVE RAPIDLY IN BRAZIL AFTER NEW DAM CONSTRUCTED

- story published by Science

The construction of a dam in central Brazil has spurred remarkably fast evolution of geckos in the region. In just 15 years, the lizards’ heads have grown larger—an adaptation that allows them to eat a wider assortment of insects made available by the dam’s creation. The find may portend other rapid evolutionary changes across the globe as humans continue to dramatically alter the natural landscape.  

Starting in 1996, the dam flooded a series of valleys in Brazil’s savannalike Cerrado region, creating nearly 300 islands out of what was once high ground. Many of the area’s largest lizard species disappeared from the new islands, likely because there wasn’t enough food to support their energy needs. But a small, dragonfly-sized gecko called Gymnodactylus amarali—a termite eater once common across the flooded area—persisted on at least some of them. This created an opportunity: Larger termites, which had previously been eaten by the larger lizards, were now readily available to the geckos.

But there was a hitch. The geckos had small heads—only 1 centimeter wide—and some of the termites were nearly the same size. Eating them presented a challenge, kind of like a house cat trying to put a squirrel in its mouth.

To figure out whether the geckos were able to adapt, Mariana Eloy de Amorim, an evolutionary ecologist at the University of Brasília, and colleagues collected some animals on five of the islands in 2011 and compared them with geckos collected at five locations along the edge of the dam’s reservoir, habitat that was not isolated by flooding. They measured the size of the geckos and, after euthanizing them, cut open their stomachs to figure out what they had been eating. 

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MEET THE ONLY ANIMAL KNOWN TO PUMP BLOOD WITH ITS GUTS

- story published by Science

High school biology classes teach us that the circulatory system pumps blood and the digestive system pumps food. But sea spiders apparently skipped that lesson: They pump blood using their guts. Researchers discovered the remarkable physiological strategy after injecting dye into sea spiders—common inhabitants of the world's oceans named for their resemblance to land-based spiders—and watching the flow of blood. They noticed that the animals’ hearts were beating weakly. But the digestive system—which is unusually extensive in sea spiders, running down each leg—was contracting in waves, moving food in the gut as well as blood in the surrounding hemocoel cavity, the spider equivalent of veins and arteries. 

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SPIDERS LURE BEES FOR DINNER BY MAKING FLOWERS LOOK FLASHIER

- story published by New Scientist

Ambush hunters normally rely on the element of surprise, opting to stay hidden until the moment of attack. But some spiders go for a flashier strategy. They reflect UV light, which makes the flowers they sit on appealing to bees – a bizarre strategy that has evolved multiple times in crab spiders, which ambush their prey instead of catching it in webs.

Felipe Gawryszewski at the Federal University of Goiás in Brazil and his team collected individuals from 68 species of crab spider in Australia, Europe and Malaysia. All of the species hunted insects using a sit, wait and pounce strategy, but some did so on drab substrates like bark and leaves while others hunted on flowers.

Using genetic information from all these species, the team pieced together a “family tree”, which showed that the flower-based hunting strategy evolved multiple times. What’s more, flower-dwelling crab spiders reflected more UV light than non-flower dwellers.

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ISLAND SCRUB-JAYS ON THE OUTSKIRTS OF SANTA CRUZ ISLAND HAVE LOWER GENETIC DIVERSITY

It's not easy living on the edge—of a species' range, that is. Preferred habitat tends to be more sparsely distributed and of lower quality. Population densities tend to be lower. And genetic diversity can be an issue because of the stochasticity associated with evolution in small, isolated populations (i.e., genetic drift).

Many organisms have reduced genetic diversity towards the edge of their range. But the vast majority of known cases involve species with continent-sized geographic distributions (e.g., the Canada lynx), and it's not clear the degree to which the same problem exists for species with more limited distributions.

In a recent study my colleagues and I published in the journal Heredity, we document the same pattern—reduced genetic diversity towards the edge of a species' range—in a bird restricted to a single island. After catching over 500 Island Scrub-Jays across Santa Cruz Island, the species' only home in southern California, we found that individuals were more homozygous towards the outskirts of the island. This was surprising (even to us) given that the species is composed of a single population and there's no evidence that certain parts of the island are closed off to dispersal from other parts of the island.

Low genetic diversity is troublesome from a conservation perspective because it could negatively impact the fitness of individuals (inbreeding depression) and/or the evolvability of populations (e.g., evolutionary responses to climate change). Our results show that even within a single population, the processes affecting genetic diversity may vary depending on where you look on the landscape.

A charismatic Island Scrub-Jay was featured on the front cover of the issue that our research appeared in:

KM Langin, TS Sillett, WC Funk, SA Morrison, and CK Ghalambor. 2017. Partial support for the central–marginal hypothesis within a population: reduced genetic diversity but not increased differentiation at the range edge of an island endemic bird. Heredity 119: 8-15 [link]