Hawthorns to apples, flies to parasitoids – how new species create more species
Scene from Goodwill Hunting where Matt Damon boasts of the awesomeness of sequential speciation.
What determines species diversity?
This is one of the most important questions facing biological sciences. It turns out that species themselves may create new biodiversity. The idea is rather simple: as new species colonize and adapt to new environments, they create new opportunities for other organisms to colonize and adapt, potentially setting off a chain reaction of adaptation events within communities and across ecosystems. The process, referred to as “sequential” or “cascading” divergence, has been hypothesized to help explain a number of biological patterns including periods where there has been an explosion of new species following mass extinctions and the inordinate amount of species diversity found in tropical environments.
Do we observe sequential speciation in nature?
If we knew of a plant-feeding insect that recently diverged – split into new species – then we could look to see if their parasitoids have followed, also diverging into new species. Well…about 400 years ago, domesticated apples were introduced from Europe to the United States. These new apples did not go unnoticed by some of the locals. A species of fly that had long been living in the US that fed on the fruits of hawthorn plants (Rhagoletis) started laying eggs in apple fruits, and before long, the species had begun to split into two diverging lineages – one that still fed on the hawthorn plants and another that fed on the newly introduced apples.
What kept these diverging flies from merging back into one species? Well, the hawthorn and apple fruits produce different chemical signals (they basically smell different) and the flies evolved to use these differences to find their “favorite” host. Because the flies mate on their host plant, apple-loving flies only mated with apple-loving flies while hawthorn-loving flies only mated with hawthorn-loving flies. Over time, the two forms mated less and less and began to become genetically different. Also, the fruits develop at different times of the year, so the flies had to adjust their internal clocks to match when their food was available. That is they evolved (adapted) to match the timing of their host. Those best synchronized to their host, whether it be apple or hawthorn, had the highest fitness – passing on more descendants with similar traits – until they now not only differ in what smells they like, but when they are flying around looking for mates. Because they began to start mating at different times of the year, those who chose apple became less and less likely to mate with those that stuck with hawthorn. Crazy enough, all of this has actually occurred multiple times in other closely related flies, adapting to other plants, such as blueberries, snowberries and dogwoods.
So, did the parasitoids split into new species, like their fly hosts?
The study "Sequential Divergence and the Multiplicative Origin of Community Diversity" published in PNAS can be found at: www.pnas.org/content/112/44/E5980.abstract
Interview with break thru radio's third eye weekly (note there are some curse words in the segment)
We recently did an interview with Lisa Autz and Zach Schepis from Break Thru Radio's Third Eye Weekly about our project. Break Thru Radio is a NY based radio show with about 3 million listeners. They are the largest internet radio station catering to under 28-year-old listeners (82% of their audience is under this age).
You can check out the podcast (we are the 3rd segment): http://www.breakthruradio.com/…
or you can check out entire video interview: https://www.youtube.com/watch?v=9a6Hc5rX2gA
Invasion biology: a very brief history
Article by Dr. Matthew A. Barnes
Charles Elton opened his 1958 text by explaining, “Nowadays we live in a very explosive world, and while we may not know where or when the next outburst will be, we might hope to find ways of stopping it or at any rate damping down its force.” Given the timing of publication, one might assume that this was an introduction to the growing political crisis that would come to be known as the Cold War. However, Elton, a zoologist at Oxford University, was referring to “ecological explosions,” dramatic increases in biological populations including disease epidemics and outbreaks of agricultural pests and weeds. The book was The Ecology of Invasions by Animals and Plants, and it would go on to be considered a seminal resource in the study of biological invasions.
Even by 1958, Elton recognized that globalization and associated increases in trade and travel were promoting biological invasions, the intentional or accidental movement of organisms out of their native range and introduction someplace new, where they can have negative impacts on the local environment and economy. Infamous invaders include jumping Silver Carp in North American rivers, stinging fire ants in the southern United States, and literal herds of rabbits in Australia, among many others. Today, the cost of biological invasions has become massive. It is estimated that invasions cost over $120 billion each year in the United States alone, and although difficult to express in dollar values, invasive species rank among the top drivers of global species extinctions.
So what can we do about invading armies? Biological invasion is the result of an unfortunate chain of events beginning with organisms accessing transport out of their native range (which can be accidental as in the case of small aquatic organisms being captured in a ship’s ballast tank or intentional as in the case of flowering plants being farmed and transported for garden sales), surviving transport and being released in a new habitat, establishing a self-sustaining population in that new habitat, and causing ecological and economic impacts. Recognizing this process, efforts can target specific links in the chain: preventing organisms from accessing and surviving transport, detecting introductions early so they can be eradicated before negative impacts manifest, and controlling the spread of invaders to minimize further damage. Because it would be logistically difficult and ethically abhorrent, we cannot incite invasions to tailor opportunities to study the ecology and management at each stage in the process. But we can study ongoing invasions (like in the Pieris project!) to gain knowledge that will help manage in the present and prevent future invasions.
Dr. Matthew Barnes is an Assistant Professor in Natural Resources Management at Texas Tech University and an editor of a blog he co-founded about how to combat invasive species by eating them - Invasivore.org. His research focuses on improving our ability to detect and predict the spread of ongoing biological invasions. When he’s not studying or cooking invasive species, he enjoys relaxing at home with his wife and kitty, playing hockey, and tasting new beers.
One of our citizen scientist's Ansel Oomenn raised some cabbage whites this summer and noticed how variable the color of their chrysalis can be. Being a little inquisitive, he did a little experiment to see how the colors in the caterpillars environment might affect the color of their chrysalis. This is something called "phenotypic plasticity" (an organisms phenotype - how it looks and behaves - can be altered by its environment) and has been observed in many other butterflies. He placed different colored tissue paper (green or white) or different materials - cardboard and potted plants - at their pupation site (where they turn from a caterpillar to a chrysalis) and he found... it did influence their color!
From our post on Invasivore.org: Sometimes the net is mightier than the fork (longer version)
Invasivore.org has had fun developing novel ways to engage the public with invasive species, but what do you do with those invasives that aren’t so filling? Answer: Put down your fork and pick up your butterfly net! We’ll at least when the invasive is a butterfly. Invasive species are not only tasty, but can be useful to study how organisms adapt to new environments and climate change. This has led a group of PhD students (us!) to use an invasive butterfly species to do some good…science! By understanding how an invasive butterfly – the cabbage white (Pieris rapae) – has adapted as it spread across North America, they can gain insights as to how other butterflies may adapt to similar environmental changes. The citizen scientist creation they are calling “Pieris Project,” is a partnership with the public (you!) to collect this invasive butterfly from across the US, and soon the world! But, they are just getting started and need your help.
The cabbage white is believed to have invaded the entire US and most of North America as well as many other parts of the world including Australia, New Zealand, and Japan; it’s pretty much everywhere but Antarctica. In North America, it all began in the late 1800s, as the butterflies were introduced from Europe and spread from eastern Canada across North America within only a few decades (there is also some evidence that there may have even been a few that invaded even earlier than the 1800s with the help of the Spaniards!). The caterpillars feed on many of our agriculture crops (plants in the mustard family such as broccoli, cabbage, kale and brussels sprouts), which is in part why they have been able to invade many parts of the world; these invasives are eating our food!
This year, the Pieris Project wants to collect at least 20 butterflies from each US state and as many countries from across the world as they can. Helping them reach this goal is easy, partly because these butterflies have invaded everywhere, including your backyard! To get involved is easy: visit the website (pierisproject.org) to learn how to catch them, where to send them and what cool things we hope to learn about these butterflies, such as: How are these butterflies adapting to changes in their environment? Where did this butterfly really come from – was it introduced from multiple countries and have they invaded multiple times? In order to answer these questions, and many more, they need your help. By catching a few from where you live you can join the many citizen scientists that are helping to use this invasive species to learn how other native species of butterflies will respond to changes in their environment, such as climate change, habitat destruction, and changes in land-use (e.g., effects of excess nitrogen in the environment).
many diverse authors write these articles