Experiences in Integrative and Comparative Biology
SICB members like a good story about an expedition, a field experience, a lab experiment, or another researcher! To spice up our newsletter, I have asked some of the leaders of SICB to relate one or two experiences that might be of interest to the membership. President Sally Woodin and President-elect John Pearse have provided us with some great examples of truly integrative and comparative biology.
Lou Burnett, SICB Secretary
Sally Woodin, SICB President
I am currently on sabbatical having a wonderful time doing research and recovering from being both President of SICB and Chair of my department, not a clever move and life is much improved now that I am merely the former. One project that I am doing in collaboration with David Wethey with support from the Office of Naval Research involves measurement of the rates at which large infauna, the organisms that live in sediments, modify their habitat. Just to put this in perspective, these biogenic rates are major forces in rather important processes such as bacterial growth rates, remineralization rates, porewater movement and exchange, acoustic properties of sediments, recruitment of infauna, predation, etc., thus working on feculence and other organism byproducts has potentially important implications. We have succeeded in using pressure sensors to measure the hydraulic activities of the large infauna.
Almost all organism activities within sediments alter porewaters since due to the properties of many sediments, organisms must pump water into the sediment in order to move within it. This changes the pressure in the porewater which we can measure and the form of the pressure wave is uniquely associated with different behaviors so one can essentially spy on the infauna, categorize the frequency of different behaviors etc using pressure sensors both in the field and in the laboratory. As an experimental tool this is an outstanding advance, allowing us to manipulate the habitat and monitor responses without destructive sampling. As an advance in the behavioral analysis of infaunal activities, it has revolutionized my view of their activities, the degree to which individuals interact below the sediment surface, and the importance of those interactions. Some photos of our recent work show that we succeeded in measuring the hydraulic head caused by these infaunal activities, measurements which allow calculation of advective porewater flux.
John Pearse, SICB President-elect
The integrative and
comparative underpinnings of my Antarctic research
I suspect that all of
us have suffered through the interminable graduate seminars in which
a professor selects a series of papers, and each week one student is
on the spot, summarizing the paper of the week while a few others
criticize. Most participants just try to get through it, rarely
participating. I conducted such seminars throughout my teaching
career, often thinking back to the first one I experienced myself as
a first-year graduate student at Stanford University in 1959.
The professor of that
seminar class, Arthur Giese, who turned out to be my major professor
and to whom I will be forever indebted, had selected papers that he
had used the previous year to write the seminal review on a
little-studied topic: reproductive rhythms of marine invertebrates. I
recall the sessions as deadly dull; Giese rarely spoke and only a few
student participants had anything insightful to say. I hardly spoke
at all. On the other hand, I found the topic, and what little was
known about it, fascinating. It was global in scope and few attempts
had been made to develop unifying principles. At the time, most work
on the problem had been done in the North Atlantic, where strong
seasonal sea-temperature fluctuations correlated well with seasonal
reproductive rhythms. A few experiments had been done on oysters and
barnacles demonstrating that change in sea temperature could change
the timing of reproduction. Ergo--- changes in sea temperatures were
thought to be all important in regulating the timing of reproduction.
Trouble was there were scattered reports that some species in
topical, polar, and deep seas, where sea temperatures were unvarying
year round, had seasonal reproduction. But the reports were sketchy
and generally questionable.
A chance to work at
McMurdo Station in the Antarctic offered me the opportunity to
examine in detail reproduction of selected polar species. I grabbed
it, and spent 14 months there, 1960-1962. Not only did I document
reproductive seasonality in several species, but I also followed
changes in biochemical composition to show a variety of integrated
seasonal changes. These findings led to my working on comparable
tropical species, particularly in the Gulf of Suez where marked
seasonal changes in sea temperatures occur, and finally in
California, where I could demonstrate with some of my students that
photoperiodism is a major factor regulating seasonality of
reproduction in sea stars, sea urchins, shrimps, and worms. That work
led to a return to the Antarctic to show, not unexpectedly, that
photoperiodism is important there as well.
The big surprise in
1961 came when I found that the focal species of my research, the sea
star Odontaster validus, produced larvae that looked for all
the world like pelagic planktotrophs. One of the few established
ideas at the time was that conditions in polar seas were much too
severe for pelagic larvae of any kind to survive, and phytoplankton
was present for too short a period during the summer to support
feeding larvae. Moreover, I found that O. validus spawns in
mid-winter when no phytoplankton is produced at all. I sat on my
finding for nearly 8 years before publishing it, and when I did I
suggested that the larvae must be benthic. It wasn't until the
mid-1980s that I had a student (Sid Bosch) who was interested in
spending a year at McMurdo to re-examine these larvae. His work with
me established the fact that the proportion of species with pelagic
larvae in the Antarctic was similar to that in other parts of the
world. There is no latitudinal gradient in the proportion of species
with non-pelagic larvae as had long been believed. Later
collaboration with Sid, Richard Rivkin, Donal Manahan, and our
students, established that the metabolic rate of polar larvae is
extremely low, so that very little food is needed to support them.
Moreover, the larvae have the ability to feed on bacteria, which are
much more evenly distributed throughout the year, as well as
(probably) dissolved organics. Nutrition of larvae also is not a
problem as previously supposed.
But if that is the
case, why are several large clades of species without pelagic larvae
present in Antarctic seas? These clades fueled earlier ideas that
severe polar conditions selected against pelagic larvae. Comparing
the abundance of brooding species in different parts of Antarctic
seas, Sid Bosch and I saw that they occur mainly in Subantarctic
waters, particularly in the Scotia arc area between South America and
the Antarctic Peninsula. This clue alerted us to the possibility that
speciation of brooders might be occurring there, where the powerful
Antarctic Circumpolar Current has been flowing in one direction for
some 30 million years. That is a lot of time for individuals of
brooding species to be wafted to new locations, founding new species
nearly upon establishment. This idea, published in 1994, has now been
strongly supported by the work of my last student, Susanne Lockhart
(co-sponsored with Rich Mooi), who has shown with molecular analyses
that the speciose, Antarctic clade of brooding cidaroid sea urchins
has been accumulating species for 30 to 40 million years (long before
the area cooled), while sister brooding clades north of the Antarctic
Circumpolar Current, in South America and New Zealand, have not.
These studies have
utilized a wide range of approaches and techniques, both in the field
and lab, that are both integrative and comparative. Indeed, they
could not have been done any other way. And they all began for me
with what at the time appeared to be a deadly dull graduate seminar
to somehow get through. I'm still in it.
Pearse, J.S. 1965. Reproductive periodicities in several contrasting
populations of Odontaster validus Koehler, a common Antarctic
asteroid. Antarctic Research Series 5:39-85.
Pearse, J.S. 1969. Slow developing demersal embryos and larvae of the
Antarctic sea star Odontaster validus. Marine Biology
Pearse, J.S. and I. Bosch. 1986. Are the feeding larvae of the
commonest Antarctic asteroid really demersal? Bulletin of Marine
Pearse, J.S., D.J. Eernisse, V.B. Pearse, and K.A. Beauchamp. 1986.
Photoperiodic regulation of gametogenesis in sea stars, with evidence
for an annual calendar independent of fixed daylength. American
Pearse, J.S., J.B. McClintock, and I. Bosch. 1991. Reproduction of
Antarctic benthic invertebrates: tempos, modes, and timing. American
Pearse, J.S. 1994. Cold-water echinoderms break "Thorson's rule."
In: Reproduction, Larval Biology, and Recruitment in the Deep-sea
Benthos, K.J. Eckelbarger and C.M. Young, eds., pp. 26-39.
Columbia University Press, New York.
Pearse, J.S. and I. Bosch. 1994. Brooding in the Antarctic: Östergren
had it nearly right. In: Echinoderms Through Time, B. David,
A. Guille, J.-P. Féral, and M. Roux, eds., pp. 111-120.
Hoegh-Guldberg, O. and J.S. Pearse. 1995. Temperature, food
availability, and the development of marine invertebrate larvae.
American Zoologist 35:415-425.
Pearse, J.S. and I. Bosch. 2002. Photoperiodic regulation of
gametogenesis in the Antarctic sea star Odontaster validus
Koehler: evidence for a circannual rhythm modulated by light.
Invertebrate Reproduction and Development 41:73-81.
Pearse, J.S. and S.J. Lockhart. 2004. Reproduction in cold water:
paradigm changes in the 20th century and a role for cidaroid sea
urchins. Deep-sea Research II 51:1533-1549.
Lockhart, S.J. 2006. Molecular evolution, phylogenetics, and
parastism in Antarctic cidaroid echinoids. Doctoral dissertation,
University of California, Santa Cruz.