Haplodiploidy

Haplodiploidy is a  mechanism of sex determination that is common in the hymenoptera but also found in some other groups. In this system sex is determined by the number of sets of chromosomes an offspring receives. Fertlized eggs develop as females, and unfertilized eggs develop as males. This means that the males have half the number of chromosomes that a female have - hence the name haplodiploidy for this system. In this system males have no father and cannot have sons, but have grandfathers and can have grandsons (think about it). Also because males are already haploid all the sperm they produce is identical.

Haplodiploidy has important consequences that seem to affect social behavior. Here's a nice description form an online Animal Behavior textbook:

1. If a queen mates only once, her daughters are highly related to each other (called supersisters), because the father's sperm are all identical.
2. A female is more related to her sisters (on average, 75% similar) than she is to her own daughters (on average 50% similar).
3. A female is more related to her son (50 % similar) than she is to a brother (on average, 25% similar).

These three factors combine to create a condition in which it may be more advantageous, evolutionarily speaking, for a female to help her mother produce sisters (to the female in question) than to produce her own daughters. Thus haplodiploidy opens the way for the evolution of a worker caste, devoted to helping their mother. If workers evolve under these conditions, then we would expect:

• That all workers will be female (males have no special pattern of relatedness in a haplodiploid system that would make working advantageous to them
• That workers will help their mother to lay and rear females, but
• That workers would prefer to lay their own male offspring, rather than rear brothers

In fact, Hymenoptera workers are uniformly female and conflict between the queen and the workers over who lays the males eggs in a nest is common. The role of haplodiploidy in the evolution of worker Hymenoptera fits into an overall theory of how genetic similarity affects social behavior called kin selection which was developed by Bill Hamilton.

Seed Plant Phylogeny

You may be surprised to find out that the relationship between the angiosperms and the gymnosperm groups is still subject to much debate. One of the perennial questions is the position of the gnetophytes.

 One of the reasons for this debate is that the Gnetophytes (one of the gymnosperm taxa we discussed) show several features that are typically associated with the angiosperms, including double fertilisation and vessel elements in their vascular tissue. Do these indicate a close relationship and that the gnetophytes are a sister taxa to the angiosperms or are they the results of parallel evolution?

Wikipedia actually has a nice clear discussion of the alternative hypotheses or for a meatier discussion there's this paper from 2009 in the American Journal of Botany:
Phylogenetic relationships among seed plants: Persistent questions and the limits of molecular data

The Evolution of Sex Chromosomes

Sex chromosomes have arisen independently in many taxonomic groups. It is an interesting question whether the same mechanisms were involved each time.

Sex chromosomes are an oddity in flowering plants. They are limited to dioecious species and only a few examples are known. The genus Silene, which includes the White Campion, includes both dioecious and hermaphrodite species and three of the dioecious species, Silene dioica, S. latifolia, and S. diclinis,  have an X-Y sex-determination system where Y specifies maleness.
Although the X-Y system evolved quite recently in Silene (less than 10 million years ago) compared to mammals (about 320 million years ago), our results suggest that similar processes have been at work in the evolution of sex chromosomes in plants and mammals, and shed some light on the molecular mechanisms suppressing recombination between X and Y chromosomes.

Ref:  Nicolas M, Marais G, Hykelova V, Janousek B, Laporte V, et al. (2005) A Gradual Process of Recombination Restriction in the Evolutionary History of the Sex Chromosomes in Dioecious Plants. PLoS Biol 3(1).

There's a synopsis of the article in the same issue: Evolution of Sex Chromosomes: The Case of the White Campion.

Debating Darwin

I only just heard about this conference which is going on next weekend right here ar UCSB. It's free to attend but they do request that you register: http://www.philosophy.ucsb.edu/conferences/

UC Santa Barbara Department of Philosophy Announcesa Steven Humphrey Fund for Excellence in Philosophy ConferenceDebating Darwin: Philosophical Issues in Evolution and Natural Selection
February 18-20, 2011

Friday, February 18

5:00 - 7:00 PM Peter Godfrey-Smith (Harvard), "Origin Explanations" 
7:00 - 9:00 PM Reception/Buffet, UCSB Faculty Club

Saturday, February 19

9:30 - 11:30 AM Elisabeth Lloyd (Indiana), "Adaptationism in Action"
11:30 - 1:00 PM Lunch, Graduate Student Association Lounge
1:00 - 3:00 PM Paul Griffiths (Sydney), "How Evolution Tracks Truth"
3:00 - 3:15 PM Break
3:15 - 5:15 PM Jerry Fodor (Rutgers), "From the Darwin Wars"

Sunday, February 20

9:30 - 11:30 AM Mohan Matthen (Toronto), TBA
11:30 - 1:00 PM Lunch, UCSB Faculty Club
1:00 - 3:00 PM Richard Boyd (Cornell), "Evolutionary Theory as Methodological Anesthesia: Methodological and Philosophical Lessons from Evolutionary Psychology"
3:00 - 3:15 PM Break
3:15 - 5:15 PM Alex Rosenberg (Duke), "How Jerry Fodor Slid Down the Slippery Slope to Anti-Darwinism, and How We Can Avoid the Same Fate"
Location: All talks will be in Theater & Dance 1701

Hidden Leg of an Ancient Snake

No, not an unreleased Jim Morrison poem, but a headline on ScienceDaily today reporting on the latest imaging of a 95 million year old snake fossil published in the Feb. 8, 2011 issue of the Journal of Vertebrate Paleontology.

A novel X-ray imaging technology is helping scientists better understand how in the course of evolution snakes have lost their legs. The researchers hope the new data will help resolve a heated debate about the origin of snakes: whether they evolved from a terrestrial lizard or from one that lived in the oceans. New, detailed 3-D images reveal that the internal architecture of an ancient snake's leg bones strongly resembles that of modern terrestrial lizard legs.

All your fly base are belong to us

Just to clarify, there are over 1,000 species of endemic Drosophila (fruit flies) on the Hawaiian Islands. These are all thought to have descended from a single introduction 26 million years ago.

Over one hundred of these Drosophila species are members of the 'picture wing group'. The figure I showed in class just depicts the hypothesized dispersal events necessary to create the 112 members of the picture wing group. Although the picture wing species are quite distinct from each other in morphology, pigmentation, and behavior it is now known that this explosive adaptive radiation occurred with relatively little change in DNA sequence. These factors make the Hawaiian Drosophila an important model system for analysis of evolutionary processes at the species level.

Learn more at FlyBase - A Database of Wing Diversity in the Hawaiian Drosophila

Speciation in action

The National center for Science Education currently has an excerpt from The Origin Then and Now: An Interpretive Guide to the Origin of Species available as a free preview:

Evolution Today: The mosquitoes of the London underground

This excerpt describes a wonderful example of speciation in action that I'm sure Darwin would have loved.

Public use of the London Underground began on January 10, 1863. That date, or perhaps some earlier date when the tunnels were being readied for traffic, marks the beginning of the path toward the formation of a new species of mosquito. We often wonder how long it takes to form a new species; Darwin speculated timescales on the order of tens of thousand to hundreds of thousands of generations. The mosquitoes of the London Underground show that if conditions are right, the process can be much faster.

Well worth a quick read. The original research paper on which this chapter is based is Culex pipiens in London Underground tunnels: differentiation between surface and subterranean populations.

Orchid moth in action

Cool, people have been posting! I'll just leave you with this video of the orchid and moth I mentioned today. Complete with a Darwin recreation and a very excited Phil DeVries

Viral Eukaryogenesis

One of the things I love about biology is how quickly you can fall down the rabbit hole. One minute you are checking something in a textbook, it raises a question, you search for an answer and suddenly you are in a strange and less certain world that makes you go whoa. Case in point - which other organelles might have an endosymbiotic origin? Last year I blogged about the peroxisome. This year it's the turn of the nucleus. Yes, the nucleus itself.

Viral Eukaryogenesis: Was the Ancestor of the Nucleus a Complex DNA Virus?

This paper, from 2001, has been cited 60 times since then (thank you Web of Science), so it has attracted some attention but not a huge amount. Looking at the titles of some of the citing papers it is clear that this whole question is now wrapped up in the question of viral origins and our friend the mimivirus again.

In the light of evolution

Posting to a blog every day is an interesting exercise. I'm reluctant to say it has made me a better writer but it has certainly helped me overcome a degree of writers block and procrastination. It also tends to permeate everything I do so I'm constantly on the look out for relevant items to post. Sometimes they just fall into my lap though. Like this article I found on the NCSE website whilst looking for something else. It's an excerpt from a forthcoming book In the Light of Evolution: Essays from the Laboratory and Field. Because the book is a series of chapters by different authors this chapter, by the science writer Carl Zimmer, can be read on its own. It makes a perfect follow up to our lecture on Darwin.

Darwin Under the Microscope: Witnessing Evolution in Microbes by Carl Zimmer

Rubbish flyers

R. L. Nudds, G. J. Dyke. Narrow Primary Feather Rachises in Confuciusornis and Archaeopteryx Suggest Poor Flight Ability. Science, 2010; 328

The fossil birds Archaeopteryx and Confuciusornis had feathered wings resembling those of living birds, but their flight capabilities remain uncertain. Analysis of the rachises of their primary feathers shows that the rachises were much thinner and weaker than those of modern birds, and thus the birds were not capable of flight. Only if the primary feather rachises were solid in cross-section (the strongest structural configuration), and not hollow as in living birds, would flight have been possible. Hence, if Archaeopteryx and Confuciusornis were flapping flyers, they must have had a feather structure that was fundamentally different from that of living birds. Alternatively, if they were only gliders, then the flapping wing stroke must have appeared after the divergence of Confuciusornis, likely within the enantiornithine or ornithurine radiations.

Or, as ScienceDaily summarized: The evolution of flight took longer than previously thought with the ancestors of modern birds "rubbish" at flying, if they flew at all, according to scientists.

Your inner fish

I just finished reading Neil Shubin's book 'Your Inner Fish.' It is a very easy and highly recommended read. We tend to focus on those areas where we have 'improved' on our fish-like ancestors (walking upright, doing pushups, inventing calculus etc) but what I found fascinating, and relevant to class today, was a discussion of olfaction (smelling) and how it's all been downhill since our aquatic past.

The human genome only contains about 23,000 protein-coding genes - which itself is an amazing fact. The other 98.5% of our genome consists of non-coding genes, regulatory sequences, introns and endogenous retrovirus sequences.

About 1,000 of those 23,000 protein-coding genes code for different odor receptors but less than half of them are functional in modern humans. Which says a lot about the importance of different senses in the evolution of humans from an aquatic ancestor (smell) to a terrestrial life (vision). Our evolutionary history is revealed in our genes.

Horizontal gene transfer

A couple of recent papers are providing good evidence for the horizontal transfer of genetic material between species.

In the Journal Nature this week: A role for host–parasite interactions in the horizontal transfer of transposons across phyla.

The horizontal transfer (HT) of genetic material between non-mating species, common in bacteria, is increasingly being recognized as a significant force in eukaryotic evolution. Most instances of HT described so far in metazoans involve mobile genetic elements — mainly transposons — but the mechanisms enabling this exchange between widely divergent species are unknown. Gilbert et al. now show that transposable elements spread between disparate species by hitch-hiking in the genomes of parasites shared by these species. Specifically, Rhodnius prolixus, an insect that feeds on the blood of tetrapods and which is the vector of Chagas disease in humans, carries four distinct transposon families in its genome that can invade the genomes of a range of tetrapods including the opossum and squirrel monkey. One of these transposon families is also present in the pond snail Lymnaea stagnalis, a vector of trematodes infecting many vertebrates.

A paper in Nature earlier this year revealed that horizontal gene transfer has also been important in the evolution of virulence in Fungi: Comparative genomics reveals mobile pathogenicity chromosomes in Fusarium

Fungi of the genus Fusarium are important plant pathogens, causing various blights, root rots and wilts. While some species have a wide host range, others are more selective. Comparative genomics of three Fusarium fungi with broad and narrow host range, two newly sequenced, provide clues as to what drives these differences. Experimental follow-up shows that simply by mixing two strains on standard growth medium, transfer of two whole chromosomes from a Fusarium oxysporum tomato pathogen turns a nonpathogenic strain into a pathogenic one. These findings shed light on the evolution of host range and pathogenicity.

Competition Drives Big Beaks Out of Business

The Darwin's Finch story I briefly mentioned is a fascinating part of a long term study by husband and wife team Peter and Rosemary Grant. They now have an amazing 37 year data set on these small birds on the Galapagos.

One of the latest parts of the story to be revealed was published in Science in 2006 as Evolution of Character Displacement in Darwin's Finches. It's also included in their news summary as Competition Drives Big Beaks Out of Business.

I think the fascinating part of this story is that it is the interaction of environment and competitors that drives evolution. Whilst resources are plentiful competition is weak but during the drought the effects of competition became severe.

Here we report that a Darwin's finch species (Geospiza fortis) on an undisturbed Galápagos island diverged in beak size from a competitor species (G. magnirostris) 22 years after the competitor's arrival, when they jointly and severely depleted the food supply. The observed evolutionary response to natural selection was the strongest recorded in 33 years of study, and close to the value predicted from the high heritability of beak size. These findings support the role of competition in models of community assembly, speciation, and adaptive radiations.

Anaerobic metazoan

Sandwiched between 'Earliest known Led Zeppelin recording' and 'Evolutionary Psychology Bingo' on BoingBoing is A multicellular organism that lives without oxygen.

This is based on a paper in BMC Biology entitled The first metazoa living in permanently anoxic conditions.

This is the first evidence of a metazoan life cycle that is spent entirely in permanently anoxic sediments. Our findings allow us also to conclude that these metazoans live under anoxic conditions through an obligate anaerobic metabolism that is similar to that demonstrated so far only for unicellular eukaryotes. The discovery of these life forms opens new perspectives for the study of metazoan life in habitats lacking molecular oxygen.

Still running

Alice in Wonderland Barbie and friends.

As we come to the end of our first quarter I think it's time we returned to the Red queen hypothesis. Although much data is consistent with the red queen hypothesis and it helps explain numerous phenomena, it has been hard to directly test it because of the time scales involved with evolutionary processes.

However in Nature recently a group of workers from the University of Liverpool (and elsewhere) used experimental populations of bacteria and their viral pathogens to directly test the hypothesis.
Antagonistic coevolution accelerates molecular evolution
(T)he rate of molecular evolution in the phage was far higher when both bacterium and phage coevolved with each other than when phage evolved against a constant host genotype. Coevolution also resulted in far greater genetic divergence between replicate populations, which was correlated with the range of hosts that coevolved phage were able to infect. Consistent with this, the most rapidly evolving phage genes under coevolution were those involved in host infection. These results demonstrate, at both the genomic and phenotypic level, that antagonistic coevolution is a cause of rapid and divergent evolution, and is likely to be a major driver of evolutionary change within species.

You'll believe a penguin can fly

I've posted this before but I'm posting it again for two reasons. 1) You get to see penguin's 'flying' 2) the combination of soundtrack and video is truly strange. Penguin's - adorable flightless comedians of the Antarctic. Leonard Cohen - the adorable flightless poet from Canada. Put them together and you get something truly disturbing.

Pick the Pollinator

As part of the nova program First Flower, about the evolution of the earliest flowers, they have an interactive 'Pick the Pollinator' game.

You should really all get all of these right although one of them (the violet) is a little clumsily presented.

There are several interesting videos and articles at the website. I don't think you can watch the whole show but you can see a nice clip on youTube.

Proboscis prediction

I mentioned the Madagascar Star Orchid, aka Star of Bethlehem orchid, comet orchid and Darwin's orchid when we talked about evolution.

Based on the extremely long corolla (about a foot in length) the moths would need to probe to get the nectar Darwin deduced that there must be moths with extremely long tongues in Madagascar even though he never saw them:

"It is, however, surprising that any insect should be able to reach the nectar: our English sphinxes have probosces as long as their bodies: but in Madagascar there must be moths with probosces capable of extension to a length of between ten and eleven inches!" Darwin, 1862 in On the various contrivances by which British and foreign orchids are fertilised by insects, and on the good effects of intercrossing.

This photo was the Botany Photo of the day on Feb 12th and they include a link to an interesting paper in the American Entomologist entitled Darwin's Madagascan Hawk Moth Prediction that describes how Darwin's description of the orchid and proposed moth was ridiculed by some as being impossible while others suggested the long nectaries were proof of supernatural creation. Darwin and Wallace went on to explain how evolutionary processes could develop both a long-nectaried orchid species and a co-evolved moth.

Unfortunately Darwin did not live long enough to see the discovery of the moth in 1903. Although the moth was originally named "praedicta" in honor of the fact that Darwin predicted its existence the name was later, unfortunately, changed.

The moth approaches the flower to ascertain by scent whether or not it is the correct orchid species. Then the moth backs up over a foot and unrolls its proboscis, then flies forward, inserting it into the orchid's spur.

Walking with Tetrapods

This week's Nature Video is also cool, and relevant to class.

The fossilized remains of 395-million-year-old footprints in Poland have turned back the clock on the evolution of four-legged creatures, or tetrapods. The finds, reported this week in Nature, are 18 million years older than the earliest confirmed tetrapod fossils.

Scientists are getting better at getting their stories out (or at least some journals are better at presenting stores to the media in digestible form)

Read the original Article, the accompanying News and Views, related news story and listen to the Nature Podcast.