Apomixis in ferns

I've been reading an interesting article published last year (2012) in the Journal of Botany (here; subscription required) on "The Evolutionary Dynamics of Apomixis in Ferns". Apomixis is a really interesting process of asexual reproduction that is fairly common in ferns, and involves modification of two critical steps in the life cycle. First, when the sporophyte produces spores, this usually occurs via meiosis and is accompanied by a reduction (by half) of the total number of chromosomes. So if you happen to be a fern in the genus Dryopteris, with a base chromosome number of 41, your diploid sporophytes will have 82 chromosomes, and this will be reduced to the base of 41 during meiosis. If that reduction does not happen and your spores retain the full complement of chromosomes, that is known as diplospory. Those spores will then germinate into gametophytes, and rather than producing eggs and sperm via archegonia and antheridia, respectively, which go on to perform fertilization and sexual reproduction, often no sexual structures are produced at all, and new sporophytic tissue will arise from somatic (body) cells of the gametophyte itself (known as apogamy).

Apomixis and apogamy have long interested botanists because they get at a fairly fundamental question in the evolution of life - is it better to be sexually reproducing or asexually reproducing? There are advantages to both strategies, and I will do a tremendous amount of boiling down here to summarize them thus: sexual reproduction involves many processes that tend to shuffle genetic material and will lead to increased genetic diversity, which will provide raw material for natural selection. If your particular genetic makeup is well-suited to your current environment, mixing things up might not be advantageous, and reproducing asexually will be more likely to allow you to maintain the status quo. As environments change, however, having additional variation will improve the changes that a new genetic combination will be better suited to the new environment. There is a lot more to the story than this, and a huge literature on apomixis and apogamy in flowering plants, and to a lesser extent in ferns, if you're interested.

The authors of the paper I mention above have also put together a website summarizing what's currently known about apomixis in ferns, including a complete list of fern species known to be apomictic. It's a great resources if you're interested in fern reproductive strategies! Here's a shot of the site:

Finally, ferns!

You may have noticed that for a blog about ferns, fern-centric posts have been sparse here since last summer. That coincides with my move to Tucson, Arizona, and the sad fact is that I just haven't found that many ferns in the desert. I know they're here! But they aren't as easy to find as in other climates. However, I'm happy to say that I've gotten a fern fix! I just had the opportunity to spend a few days in northern Florida, and even in late February things were lush and there were ferns out in force (I'll cease the letter f-based alliteration now).

There were three ferns I kept running into during my visit, and they're a combination of things that are common in the southeastern U.S. (Deparia acrostichoides and Pleopeltis polypodioides), and in subtropical/tropical climates generally, at least in the New World (Nephrolepis sp.). Here they are:

Deparia acrostichoides:

Pleopeltis polypodioides:

Nephrolepis:

I'm confident in the species-level identification of the first two, but there are actually several species of Nephrolepis found in Florida, including a hybrid (my favorite things!). You may recognize this genus if you have a "Boston Fern" as a houseplant; it's the same genus, and the original Boston fern belongs to Nephrolepis exaltata, which is a frequent escapee in congenial climates. There's a great explanation of the Nephrolepis species of Florida, along with a detailed key, in the July/August 1996 edition of the FL Department of Agriculture and Consumer Services' Botany Circular. That link goes straight to the PDF. Unfortunately I didn't find this before leaving, so I didn't have a chance to confirm which species I was looking at, but I strongly suspect that it was N. exaltata.

And of course, it wouldn't have been a proper visit to Florida without a gator sighting:

North American Dryopteris pubs

I'm thrilled to announce that a final version of the third chapter of my PhD thesis, which was published in provisional proof version months ago, has finally been posted on the journal's website, BMC Evolutionary Biology. If you're interested in reading about the evolutionary history of the fern genus Dryopteris in North America, you can find the paper here (or here's a direct link to the PDF). BMC is a collection of open-access journals, so you can download the paper for free. If you're really interested in Dryopteris and either feel like paying for articles or are associated with a university and have library access, you can find the papers corresponding to my chapters 1 and 2 online as well. You can also email me at sessa DOT emily AT gmail DOT com and I'll be happy to send you reprints (are they called that anymore if they're not actually printed out?). Here are links to the full set of what's published thus far:

• Phylogeny, divergence times, and historical biogeography of New World Dryopteris (Dryopteridaceae) (= ch. 1). Sessa, Zimmer, Givnish 2012 AJB 99(4): 730.
• Reticulate evolution on a global scale: A nuclear phylogeny for New World Dryopteris (Dryopteridaceae) (= ch. 2). Sessa, Zimmer, Givnish 2012 MPE 64(3): 563.
• Unraveling reticulate evolution in North American Dryopteris (Dryopteridaceae) (= ch. 3). Sessa, Zimmer, Givnish 2012 BMC Evol Biol 12: 104.

I'm proud of each of these papers for different reasons, but this third one is probably my favorite, because it tells the story that got me interested in Dryopteris in the first place. This group in North America has been suspected of having undergone reticulate evolution via allopolyploidy ever since botanists started looking at them over a hundred years ago, and many hypotheses have been suggested to explain the relationships among the 13 species on this continent (see Figure 1). 

The most widely accepted of these theories involves a missing, putatively extinct diploid ancestor of several of the allopolyploids, but no one had ever tested this using DNA sequence data. Figure 6 from the paper summarizes the results of my analyses, which unequivocally supported this hypothesis, known as the "D. semicristata" hypothesis after the missing ancestor.

I also included a figure showing the range maps of these taxa up above, because the final pieces of my PhD puzzle focus on transgressive trait expression and physiological ecology of these ferns. Hopefully you can see in the maps that several of the allopolyploids have ranges that are transgressive relative to one or both parents - meaning their ranges extend beyond those of their parents. This suggests that the polyploids, which are hybrids between those parental species that then underwent whole genome duplication, likely possess some physiological or morphological features that are distinct from the parents and that have allowed them to expand their ranges and coexist at a regional level with their progenitor species. The two final papers resulting from my PhD explore these ferns' physiology using field and common garden experiments. The first is in review right now, and the second awaits publication of the first. Stay tuned for more news about that in the coming months.

Gender Gap in Science Publishing

My friend and fellow blogger Dr. Budke over at Moss Plants and More has a great post today about a study on gender in academic publishing. The research group conducting it, at the University of Washington, have access (via the archive JStor) to almost 8 million scholarly papers in a number of academic fields, from evolution to anthropology to law to classics. They decided to use this database to study gender differences in academic publishing, and have built two really excellent online viewers that allow you to peruse the data, broken up by time period and field, and showing the percentage of papers that include female authors. You can also see what percentage have women as first and last authors (the two most important author positions in academic publishing).

The data are really fascinating, and I'm happy to observe that the overall trend as you move through the three time periods (going from 1665-1970 to 1971-1990 to 1991-2010) is one of increasing female participation in publishing over all fields. The increase in the most recent two decades, compared to the 1971-1990 timeframe, is particularly impressive. What's most fun, though, is that they break things down quite finely into discipline and subdiscipline - so, for example, within the Ecology & Evolution category, there's a subcategory for Ferns! The "All years" percentages of female authors for the category and subcategory, respectively, are 18.5% and 19.7%, but within the last two decades they've risen to 22.8% and 25.9%. So fern biology publications have tended to have more female authors than the general evolution category, but we've pulled a bit further ahead in the last 20 years or so. Pretty cool! And since it was Jessica's post that alerted me to this dataset in the first place, I have to acknowledge that her field, Bryophytes, is even closer to gender parity in its publishing than we fern folks - they're at 34.1% female authors over the last two decades. Way to go Moss Plants and your people!

You can explore the data in a variety of ways at these two sites:
Women as Academic Authors, 1665-2010
Gender composition of scholarly publications (1665-2011)

Berry Go Round #56

I forgot to mention that my post on the new fern genus Gaga was included in the November issue of Berry Go Round over at Seeds Aside! Go check it out for more great plant-focused blogging content this month!

Ferns of the Central Amazon

A while back I posted about the Portuguese word samambaia, which means 'fern'. I thought about this lovely word again yesterday when a speaker in our weekly evolution seminar series mentioned a group of guides that have been published for various plant groups in the Amazon - including the ferns!

This fern key is fantastic. It covers 125 taxa found in the central Amazon of Brazil, in the Reserva Biológica do Uatumã, an almost one million hectare reserve that was built in response to the construction of a dam that had pervasive environmental impacts in the region. It is located in the northeastern corner of the state of Amazonas, not too far from Manaus. The reserve is now a resource for research and education.

Map from the Institute for Conservation and Sustainable Development of Amazonas

The fern guide is very comprehensive, and has a built in key that will allow you to use almost any feature of the plant that might be available to you, including habit, various features of the sori, and a number of characteristics of either the sterile or fertile fronds (which happily are separate categories - these folks really know ferns!).

Identification key to the ferns of Uatumã

In addition to this interactive key (which is a Java app), there are also two beautiful PDF guides that you could print out for your next Amazonian adventure. One is a PDF version of a gorgeous book, which I happened to pick up a hardcopy of at a conference a few years ago, called Guide to the Ferns and Lycophytes of Rebio Uatumã (below left). The other is a grid of photos of common ferns in the Reserve (below right). The latter would be more amenable to printing and laminating for a visit to the rainforest.

  

If you're interested in guides to other plant groups in Brazil, check out the website of the Brazilian branch of PPBio. PPBio is the Program for Planned Biodiversity and Ecosystem Research, which operates in Brazil and elsewhere. The site is in Portuguese, but the guide page has cover photos for each group that you can use to find what you're looking for. In addition to ferns they have guides for Zingiberales, Fabaceae, and also lizards.

Selaginella

I often post about non-ferns here, especially if I have particularly nice flowering plant photos I'd like to share, but today we shift to another lineage entirely: the often overlooked lycophytes! Lycophytes used to be called "fern allies" because the relationships between these two and the other groups of land plants weren't well understood. Now we know that lycophytes are the sister group to ferns plus angiosperms and gymnosperms, meaning that ferns are more closely related to conifers and flowering plants than they are to lycophytes. Lycophytes are equally related to all three, because they share a common ancestor with all of those three groups, before their three lineages diverged. Here's a family tree of the major land plant lineages that might clarify things:

On our field trip to Organ Pipe a few weeks ago, we were after lycophytes, particularly members of the genus Selaginella. These are often called "resurrection plants" because of their ability to dry down when water becomes scarce and then rapidly rehydrate when the rains return. Here's a great video, made by a fern colleague, Fernando Matos, showing a Selaginella "coming back to life":

The ones that we found haven't quite gotten to resurrecting yet... it's pretty dry out there right now. You might not notice them at first, because they're quite diminutive and rather crinkly and dried up, but once you know what to look for, you'll find that you're surrounded by a carpet of Selaginella in many of the rocky, desert-y areas around here. The lower photos here demonstrate that:

This is the type of habitat we found these guys in, rocky upslope and surrounded by various grasses, cacti, cholla, and other typical desert plants: