5 December 2006
Horned scarabid beetles have acted as a model system for polyphenic development and the evolution of extreme allometries. Recent developmental studies have begun to dissect the mechanisms through which horns develop--or not--in individuals. Horn development appears to share a surprising number of genes with appendage development, raising the possibility of the evolutionary co-option of this developmental network to a novel function. This week, let's consider two recent articles to address this issue.
Emlen, D. J., Szafran, Q., Corley, L. S., and Dworkin, I. (2006). Insulin signaling and limb-patterning: candidate pathways for the origin and evolutionary diversification of beetle 'horns'. Heredity 97(3): 179-91.
29 November 2006
The evolution of mammalian tooth cusps is one area where population level morphology studies and model system studies of development are beginning to converge. Each of these aspects in considered in the two short papers for this week. Jernvall presents a developmental model explaining variation in tooth cusps, while the article by Kassai et al. details one mechanisms by which such morphological difference might appear during evolution.
Kassai, Y., et al. (2005). Regulation of mammalian tooth cusp patterning by ectodin. Science, 309: 2067-70.
21 November 2006
Some light reading in advance of Thanksgiving: Current Biology recently ran two very short "quick guides" on evolutionary contingency and convergence. These ideas offer somewhat different spin on the history of life and are interesting to consider in light of debates on homology in development and the prevalence of gene co-option.
Conway Morris, S. (2006). Evolutionary convergence. Current Biology 16, R826-7.
While we're thinking historically, let's also consider a recent and short historical / theoretical treatment of evo-devo.
14 November 2006
The re-evolution of complex characters, once lost, is considered highly unlikely. Yet it is possible if underlying developmental mechanisms are retained. Kohldorf & Wagner present a phylogenetic study of a gymnophthalmid genus in which digit and limb reductions have been extensive. Using various methods of ancestral character state reconstruction, they conclude that these complex structures have indeed reappeared after being lost within lineages.
7 November 2006
Genetic networks mediate phenotypic development from varying genotypic states. However, investigators are still exploring the ways in which changes in genetic networks may or may not correlate with phenotypic changes. This week let's consider two recent papers: one from yeast, the other from plants; one in which phenotypes are conserved despite network divergence, the other where mechanisms and phenotype both diverge.
Floyd, S. K., and Bowman, J. L. (2006). Distinct developmental mechanisms reflect the independent origins of leaves in vascular plants. Current Biology 16, 1911-7.
31 October 2006
It's Halloween. So this week's choice for an article was easy... a selection experiment for aggressive flies. Kidding aside, genetic analysis of behavior is a growing field, and Drosophila has been a leading model.
Please join us to consider what this study and these methods reveal about the genetic basis of behavior and nervous system development.
24 October 2006
This week, Elizabeth has suggested an article which attempts to model genomic changes accompanying adaptive radiation and speciation. This study by Gavilets & Vose from PNAS emphasizes the importance of ecological opportunity and genetic constraints in controlling the dynamics of adaptive radiation.
17 October 2006
For those of you who found Antonia Monteiro's talk in EEB last week interesting or provocative, I urge you to join the discussion this week as we examine the evolution of polyphenic wing reduction in insects. As a starting point, we will consider two articles dealing with this phenomenon in ants and aphids. Baratte et al have taken a morphological and developmental genetic approach to try to understand the homology of a putatively wing-derived structure in female ants. The short review by Braendle and colleagues describes what is known about plastically induced wing dimorphism in aphids.
Braendle, C., Davis, G. K., Brisson, J. A., and Stern, D. L. (2006). Wing dimorphism in aphids. Heredity 97, 192-9.
10 October 2006
The origin of paired appendages was a major evolutionary innovation for vertebrates, marking the first step towards fin- (and later limb-) driven locomotion. Freitas et al. show that shark and lamprey median fin development involves the same genetic programs that operate in paired appendages. Despite their different embryonic origins, paired and median fins utilize a common suite of developmental mechanisms. They intrepret these results as suggesting that the molecular mechanisms for fin development originated in somitic mesoderm of early vertebrates, and that the origin of paired appendages was associated with re-deployment of these mechanisms to lateral plate mesoderm. Is this a convincing example of the co-option of a developmental mechanism?
In addition, let's consider a critique of evo-devo assumptions and methodology, which appeared this summer.
3 October 2006
This week we'll conclude our series of articles drawing from issues of evolution in pigmentation and pigment patterns. A recent article by Patricia Wittkopp reviews work done with Drosophila species pigmentation and the role that modifications to cis-regulatory elements have played in the evolution of abdominal pigment patterns in this group of insects. The article also covers what is known more broadly about the structure, function, and evolution of regulatory elements.
I hope this will be a launching point for discussions on the relative importance of regulatory and coding sequence changes in evolution, as well as other topics. Please join us for a lively conversation!
26 September 2006
Two reviews appeared this summer that cover an important area of research in evo-devo: butterfly wing pigmentation patterns. This field has a long classical history, and it continues to be very active as investigators have applied new molecular techniques, laboratory selection, and other experiments. Butterfly wing patterning systems have been used to address several issues, including evolutionary and genetic constrains, the developmental basis of pattern, adaptive phenotypic radiation and speciation, mimicry, and parallelism.
Joron, M., Jiggins, C.D., Papanicolaou, A. and McMillan, W.O. (2006). Heliconius wing patterns: an evo-devo model for understanding phenotypic diversity. Heredity. 97: 157-67.
I'm sure we will find much to discuss from this intriguing field. Please join us!
19 September 2006
Our discussion last week touched on the issues of parallel evolution and canalization. Let's consider two papers dealing with these topics. First, continuing our series of articles on pigmentation, Whibley et al. present a morphometric treatment of color variation in the snapdragon, Antirrhinum.
Last week we also mentioned the role of Pitx1 alleles in the evolution of pelvic reduction in stickleback fish. Coincidentally this week's issue of PNAS presents a new study expanding this work.
12 September 2006
Last week we discussed how the evolution of chromatophore cell behavior may have influenced the evolution of pigment patterns in zebrafish. Staying with the topic of evolution in pigmentation this week we'll look another vertebrate system, and examine a review and short, new data paper on the story of rock pocket mice.
Hoekstra, H. E., Hirschmann, R. J., Bundey, R. A., Insel, P. A., and Crossland, J. P. (2006). A single amino acid mutation contributes to adaptive beach mouse color pattern. Science. 313: 101-4.
In this system, an argument has been made that changes in mouse coat color are adaptive in predator avoidance. What is known of the underlying developmental and genetic causes of pigmentation differences, and how are these affected by local ecological and selective pressures? Please join us for discussion of a topic that truly draws on all fields of biology.
5 September 2006
This week, I'd like us to consider a relatively high-profile evo-devo story. Darwin's finches are a classic example of adaptive morphological radiation and speciation. However, attention has only recently been paid to the ontogenetic underpinnings of these divergent beak shapes. A short Nature article last month takes a candidate-gene approach to examine one of the developmental mechanisms involved.
In addition, let's discuss another vertebrate evo-devo story and start to think about the evolution of pigmentation and its patterns.
David Parichy has been doing a detailed genetic analysis of pigmentation in various zebrafish species, and this review covers much of the work on this colorful topic.
29 August 2006
While a number of interesting papers appeared this summer, let's start off by throwing in another related field, cancer research, with a broadly interesting article that's sure to generate many questions.
This article uses phylogenetic methods to analyze the epidemiology of a transmissible canine cancer, with the bizarre finding that it is propagated clonally. Also included is a brief communication from Nature earlier this year regarding a similar disease in the Tasmanian devil.