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David C. Lahti Postdoctoral Fellow Department of Biology Morrill Science Center University of Massachusetts Amherst, MA 01003
phone: (413) 577-3557 FAX: (413) 545-3243 email: lahti@bio.umass.edu |
Welcome to my professional web
page. My interests lie broadly in
the fields of biology (evolution, animal behavior, ecology), and philosophy (of
biology, morality). My central
biological research goal is to understand the evolution of complex behavioral traits
and associated morphology in an ecological context. I am especially interested in the development of learned
vocal communication, short-term evolution following species introductions, and
the dynamics of antagonistic coevolution between brood parasites and their
hosts.
I received my B.S. in biology and history at Gordon College in 1993. In 1998 I received a Ph.D. in philosophy for a study of the relationship between biological science and the foundations of morality, at the Whitefield Institute, Oxford. In 2003 I received a Ph.D. in ecology and evolutionary biology at the University of Michigan, for research on the ecology and evolution of breeding adaptations in an African weaverbird. From 2003 to 2005 I was a Darwin Fellow in the Program in Organismic and Evolutionary Biology at the University of Massachusetts. Since the fall of 2005 I have been funded by an NIH Ruth L. Kirschstein National Research Service Awards (NRSA) Training Fellowship, with Jeff Podos. Jeff and I are conducting experimental tests of a newly revised model of bird song learning.
Contents:
Main
Current Research Projects
Main
Recent and Current Teaching
Overview
of Main Research Interests
See also:
University of Massachusetts
Darwin Fellows
Reflections on Great Literature
Current and Recent Research
Projects:
· Avian brood parasite - host coevolution between the diederik cuckoo (Chrysococcyx caprius) and African weaverbirds (Ploceidae)
·
The dynamics of trait evolution under relaxed selection
·
Experimental tests of the development and function of vocal
learning in songbirds, using the swamp sparrow (Melospiza georgiana)
(with Jeff Podos
and Dana Moseley).
·
Ecology and evolution of breeding adaptations,
including short term evolution of egg appearance, in the village weaverbird Ploceus
cucullatus (dissertation research, in the UMMZ Bird Division)
· Evolutionary influences on bird egg appearance (including a collaboration with Dan Ardia)
·
Morphological and behavioral evidence for the
phylogenetic relationships of the cuckoo-finch Anomalospiza imberbis
(with R. B.
Payne)
·
Comparison of the genetic diversity of native and
introduced populations of the village weaverbird Ploceus cucullatus (with
Heather Lerner, as a
Visiting Scholar in the UMMZ Mindell Lab)
· Evolution of human moral experience and moral tension (including a collaboration with Bret Weinstein)
Selected Publications:
·
Lahti, D. C.
2006. Persistence of egg
recognition in the absence of cuckoo brood parasitism: pattern and
mechanism. Evolution 60:
157-168. Download
·
Lahti, D. C.
2005. Evolution of bird eggs
in the absence of cuckoo parasitism.
Proceedings of the National Academy of Sciences of the U.S.A. 102:
18057-18062. Download
·
Lahti, D. C. and B. S. Weinstein. 2005. The better angels of our nature: group
stability and the evolution of moral tension. Evolution and Human Behavior 26: 47-63. Download
· Lahti, D. C. 2005. The village weaverbird: marvel or menace? In R. T. Wright and B. J. Nebel, Environmental Science, 9th ed. Englewood Cliffs, NJ: Prentice Hall, p. 96. Download
·
Lahti, D. C. 2004. “You have heard… but I tell you…”: a test of the adaptive significance of moral evolution. In P. Clayton and J. Schloss (eds.) Evolution
and Ethics. Grand Rapids, MI:
Eerdmans, pp.132-150. Download
·
Lahti, D. C.
2003. Cactus fruits may
facilitate village weaverbird (Ploceus cucullatus) breeding in atypical
habitat on Hispaniola. Wilson
Bulletin 115: 487-489. Download
·
Lahti, D. C. 2003. Parting
with illusions in evolutionary ethics. Biology and Philosophy 18:
639-651. Download
·
Lahti, D. C. 2003. A case study in invasive species
assessment: the Village Weaverbird Ploceus cucullatus. Animal
Biodiversity and Conservation 26: 45-54. Download
·
Lahti, D. C. & R. B. Payne. 2003. Morphological and
behavioural evidence of relationships of the Cuckoo-finch Anomalospiza
imberbis. Bulletin of the British Ornithologists' Club 123:
113-124. Download
·
Lahti, D. C. & A. R. Lahti. 2002. How precise is
egg discrimination in weaverbirds? Animal Behaviour 63:
1135-1142. Download
·
Lahti, D. C., A. R. Lahti, & M. Dampha. 2002.
Associations between nesting Village Weavers Ploceus cucullatus and
other animal species in The Gambia. Ostrich 73: 59-60. Download
·
Lahti, D. C. 2001. The “edge effect on nest predation”
hypothesis after 20 years. Biological Conservation 99: 365-374. Download
· Lahti, D. C. 1998. An Appraisal of Naturalism in Contemporary Meta-Ethics. Ph.D. dissertation, Whitefield Institute, Oxford. Download
·
Lahti, D. C.
Pigment as parasol: a hypothesis explaining the color of blue-green bird
eggs.
·
Lahti, D. C., H. R. L. Lerner, A. R. Lindsay, and D. P.
Mindell. Genetic diversity of an
invasive bird in native and introduced populations.
·
Lahti, D. C.
Bird song and human speech;
Bird symbols in human culture;
Human effects on birds;
Similarities in vocal learning between animals and humans [4 separate
articles]. In M. Bekoff (ed.), Encyclopedia
of Human-Animal Relationships.
Westport, CT: Greenwood Publishing Group, 2006.
·
Animal Behavior (UMass. BIO550)
·
Experimental Studies of Adaptation (UMass. OEB697J)
·
Evolution: Diversity of Life through Time (UMass.
BIO280)
·
Biology and Social Issues (UMass. BIO105)
·
Bioethics (Au Sable Inst. BIOL/PHIL351)
·
Ornithology (Au Sable Inst. BIOL305)
·
Biology for Nonscientists (UMich. BIO100)
·
Introductory Biology (UMich. BIO162)
·
Evolution (UMich. EEB390)
·
Behavioral Ecology (UMich. BIO492)
·
Ornithology (UMich. EEB433)
· Independent Studies in Human Evolution and Evolutionary Theory (UMich. EEB300)
Overview of Main Research Interests:
My central research goal is to understand how complex traits are shaped in an evolutionary and ecological context. I find that two situations provide especially promising opportunities to discover patterns in trait evolution and adaptation: short-term evolution following species introduction, and coevolution. The introduction of species into new habitats can result in near-natural experiments in which to track the effects of ecological changes on traits. Coevolutionary dynamics often present intense examples of adaptation, and can simplify the identification of important sources of selection. I am particularly interested in trait suites that involve behavior because they present some of the most challenging ecological and evolutionary scenarios. Part of this challenge lies in understanding the ontogeny of behavior, so a third major component of my research is dedicated to unraveling the development of learning, and particularly the interplay between some learned traits that are highly canalized, and others that are more subject to alteration through development.
1.
Testing adaptation with species introduction
I have used African Ploceus weaverbirds as model organisms for studying the evolution of a suite of traits including egg appearance features, nest structure, egg recognition and rejection, and aggressive behavior. In Africa the diederik cuckoo Chrysococcyx caprius is an obligate brood parasite, laying its eggs in weaver nests. The cuckoo’s eggs mimic those of weavers. Such parasitism nullifies a weaver’s reproductive attempt unless the host rejects the parasitic egg. The eggs of different female village weavers are among the most variable of any bird species, but egg appearance is consistent within an individual female. In field experiments in West and South Africa I showed that patterns of egg appearance variation in the village weaver Ploceus cucullatus function in brood parasitism avoidance. Weaver females reject foreign eggs in proportion to the difference in appearance from their own eggs.
The village weaver is an abundant
species that has successfully established following introduction to new
environments that differ in important ways from its native range in
Africa. In fact, its notorious
ability to invade new habitats, conform to human settlement, and exploit
agriculture has created a concern among governments and national media in its
native and introduced ranges. I
exploited this situation to further analyze the evolution of egg appearance and
egg rejection in the village weaver.
I compared these traits in birds in their native range in Africa with
populations on islands in the Indian Ocean and the Caribbean where brood
parasitic cuckoos do not exist, and where village weavers became established
about 
100 and 200 years ago respectively. Even after such brief spans of time,
both population-level variation and within-clutch consistency decreased in the
introduced populations, resulting in poorer egg recognition in experimental
tests of those populations. The
perceptual and cognitive abilities required to recognize eggs, however,
remained latent in the introduced populations.
I have also been characterized broad-scale genetic differences between these source and introduced populations, in part to understand the likely interplay between the effects of founder events and those of selection, by the use of molecular analyses (especially DNA sequencing).
Directional evolution of egg color between source and introduced populations prompted me to write a review of the evolution of bird egg color. I have developed a general hypothesis to explain vibrant colors in bird’s eggs as protection from solar radiation. Differences among village weaver populations facilitated an initial test of this hypothesis. I am now collaborating with Dan Ardia on a series of experimental tests of the impact of solar radiation on egg thermal dynamics; and I plan to take advantage of historical introductions of other bird species for further tests of change in behavioral and associated traits.
2.
Brood parasite – host coevolution
I am impressed by the promising ways in which brood parasite - host interactions have begun to be applied to an understanding of coevolution. The similar life-histories of host and parasite, the significant selection pressure imposed by the parasite on the host, and the ease with which the interactions may be observed and experimentally manipulated, are among the features that render this system valuable from the standpoint of coevolution. The same cuckoo that parasitizes the village weaver also parasitizes several other members of the weaver family (Ploceidae) in Africa. These other host species vary in egg appearance and, apparently, in their behavioral responses to parasitism. This situation provides an excellent opportunity to use both experimentation and the comparative method to characterize coevolutionary dynamics and to investigate how antiparasite adaptations arise. To this end, I am planning a collaborative project with Mike Sorenson of Boston University and R. B. Payne of the University of Michigan, with the objective of producing a complete molecular phylogeny of Ploceidae. Meanwhile I will also be acquiring data on brood parasitism frequency, host egg variability, and behavioral responses to parasitism for several host weaverbird species in Africa. I plan to incorporate these results along with existing experimental data into a testable model of coevolution.
Molecular techniques are a growing part of my research program, and I am eager to take advantage of recent developments that continue to simplify the gathering of data that will support my research program, such as the estimation of loci involved in egg coloration. During my next field season with weavers, besides sampling for the molecular phylogeny, I will extract albumen from live eggs to assess maternity by protein electrophoresis. This data will help me to determine rates of intraspecific parasitism, which may contribute to the maintenance of egg recognition and associated traits in some weaver species.
3.
Development of vocal learning
The complexities of learning
present significant challenges to behavioral studies. Little is known, for instance, about how weavers learn the
appearance of their eggs, how the decision to reject or accept an egg is
influenced, and how much variation between individuals in egg recognition
ability is due to differences in genes.
In contrast, certain model systems, such as vocal communication in
songbirds, have provided powerful insights into learning and its development. My main current project is an
NIH-funded collaboration with Jeff Podos on the development of bird song
learning. Using swamp sparrows (Melospiza
georgiana), Podos and colleagues found that birds produce some song
variants at the end of development that differ from those they memorized
earlier. This indicates that birds
can change their templates, the 
neurological
representations of memorized song, which were thought previously to be
constant. Birds appear to
appropriate songs to their individual production abilities, for instance
dropping notes or interrupting the continuity of songs that are too rapid to
reproduce accurately. This work
has led to a revised model of song learning, and has raised the possibility of
a route to observed macroevolutionary patterns of diversity in bird song, a
phenomenon that has long fascinated students of learned vocal
communication. Podos and I are
currently testing this revised song learning model experimentally by
manipulating the acoustic input received by young swamp sparrows and monitoring
the development of their competence in song. We present birds with model songs that are modified from
species typical vocalizations in trill rate. The revised model predicts that birds will memorize atypical
songs accurately, but may modify these representations later in development in
order to optimize performance. A
further goal is to test the relationship between developmental modifications in
song features and the biological function or communicative value of those
features. I will be addressing
this by assessing natural variation and experimentally testing adult responses
to modified songs.
In addition to revealing important aspects of the development of learned vocal communication, this project may be a first step in a long-term investigation of the ways in which species differences in bird song have arisen. For instance, sexual selection over evolutionary history appears to have pushed vocal performance to its limit in some species, forcing males to modify memorized songs in ways similar to those observed in our study. These improvisations can include fundamental changes in syntax (e.g., shifting from a trilled to a phrased song) that are similar to differences between related songbird species, differences whose origins are yet unexplained.
·
Webpage
last revised 9/2005
·
Picture
credits: photography and drawing
by April Lahti except where
noted.
1. (Top of page) Stenocereus
(pitayo) desert in northeastern Dominican Republic (6/01)
2. (Contents) Drawing
of west African form of the village weaver (Ploceus cucullatus cucullatus)
(10/02)
3. (Main current research projects) Spottedbacked weaver (Ploceus cucullatus spilonotus)
in Pietermaritzburg, South Africa (11/00)
4. (Forthcoming publications) Young chacma baboon (Papio ursinus) in Kruger
National Park, South Africa (11/00)
5. (Main current and recent teaching) Golden-mantled squirrel () in Rocky Mountain National
Park, Colorado (8/04)
6. (Statement of biological research interests) Display of the West African form of
the village weaver, The Gambia (7/99)
7. (Statement of biological research interests) Eggs of different individuals
of the village weaver, The Gambia (David Lahti, 7/99)
8. (Bottom of page)
Stanhope-by-the-Sea, Prince Edward Island, Canada (8/94)
