Random Wonders of Biology

Some assorted notes taken last night. I'm not sure which, if any, will make it into the evolution book, but that doesn't matter; knowing the material conditions how I think about everything else, including things that do make it into the material. There are typos.


The main mode of corals dispersing widely is that of planula (immature coral) larvae attaching to rafts of vegetation floating in the sea. Colonies of corals may traverse 20k-40k km in their lifetime, in the Western hemisphere making several circuits of the tropical and subtropical Pacific basin. From: Helmuth, B., R.R. Veit, R. Holberton (1994). "Long-Distance Dispersal of a Subantarctic Brooding Bivalve (Gaimardia trapesina) by Kelp-Rafting." Marine Biology 120: 421-426.

Coral reef species are amongst the widest-distributed of all organisms due to dispersal of teleplanic larvae in surfae currents and transport of adults on floating rafts. Such rafts include kelp, but also the bouyant skeletons of the reef coral Symphillia agaricia measuring around 50cmx15cmx35cm, weighing about 15kg, wet. In the Great Barrier Reef area, such rafts compose ecosystems composed of filamentous algae, goose barnacles, decapod crustaceans, pearl and reef oysters, gastropods, bryozoans, and foraminaferans. These coral skeletons wash up on beaches, dry out (becoming bouyant) and then are washed to sea again, at which time they begin to accumulate the ecosysem. From: DeVantier, L. M. (1992). "Rafting of Tropical Marine Organisms on Bouyant Coralla." Marine Ecology Progress Series 86: 301-302.

A 630bp section of coral mtDNA was found to be invariant in individuals sampled from 18 populations over 3,000km from Baja California to SE Alaska. In contrast, nuclear DNA of these populations differed as expected across such a range, particularly because these species (Balanophyllia elegans) disperse only small distances, crawling briefly on the sea floor rather than, for example, riding rafts of vegetation as in some other species. The substitution rate for this species, as in others, is calculated to be about .00055 substitutions per site per year, about the same as for plants such as rice and maize. All of this supports slow mtDNA mutation rate in anthozoans; .055% per million years, or 50-100 times slower than in an array of other animals, including sharks and shrimps. From:
Hellberg, M. E. (2006). "No Variation and Low Synonymous Substitution Rates in Coral mtDNA Despite High Nuclear Variation." BMC Evolutionary Biology 6(24).

San Juan Island hermit crabs and the snails providing their shells (*most* hermits must swich out shells they normally use for protection as they grow--some species [Pagurus] occupy shells that support colonial organisms that grow continuously from the lip of the shell) were observed from 1967 to 1970. Over 4,000 snails were tagged in the 200^m study area. About half died each year, and by May 1968 the first crab using a shell was identified. Shells were 20-40mm in length. Crabs appear to select thicker shells. Most months, .5 to 1 shell became avialable per crab (crab population varied from 100-300 in the study area). Physical processes remove available but uninhabited shells. Crabs select good shells; broken or thinner shells are more suceptibel to rpedation, produce fewer eggs, and grow more slowly (p.130). More shells wer available in spring and summer than in winter. Crab population is to a degree limited by shell availability. From: Spight, T. (1977). "Availability and Use of Shells by Intertidal Hermit Crabs." Biology Bulletin 152: 120-133.

African slendter-tailed meerkats (gregarious mongooses of the species Suricata suricatta) were observed for 26 band-years over four breeding seasons. Breeding is seasonal with most births at the rainy season and females coming into new oestrus within three weeks of giving birth. Kitten mortality was largely due to cold and predation, occurring at 3-5 weeks of age. Effective foraging independence is at 12 weeks. Some instances of infanticide were inferred; they seem more to have to do with higher-ranked females killing lower-ranked offsprings' young for ranking reasons, rather than being correlated with rainfall or other environmental variables (p.316). Offspring survival can depend on many factors, including resource (vegetation and arthropod) availability due to rainfall regime, time of female investment in young (which may vary with female health at time of birthing) and climate varaition at time of gestation, lactation and the post-weaning period (p.310). Most demanding time for females is gestation and lactation, and reproduction is scheduled for this. Breeding helpers assist in rearing offspring, and can increase survival of offspring by providing food or protecting the young. In one case, an entire litter died because a tawny eagle (Aquila rapax) prevented foraging adults--and the babysitter, who had gone without food for two days and finally left the den--from returning; the kittens froze to death in the den (p.317). other birds of prey also took young. A Cape cobra (Naja nivea) entered a den once, and was repeatedly mobbed by meerkats; one male chased the snake away after it had eaten two kittens. Overall, 35% of all kittens died at den in the first 30 days after first emergence. Cold is a major killer, and kittens huddle in the den for warmth. Over 20 spp of mammals huddle for warmth (p320). When kittens were separated from babysitters, they call until they are rescued. Flooding can kill: one babysitter single-handedly moved an entire litter from a flooding den to a dry den, over 50m, while the rest of the band were away, foraging. In the first foraging behavior, when kittens leave the den at about 4 weeks, until about 3 to 6 months, predation mortality was high, but dropped significantly after this; babysitters commonly take young into the den when predators are around. Breeding was scheduled so that birth--often simultaneous among the entire band--occurs when resources are best for the period of lactation, not the period of mating. Despite work of helpers, there was no statistical effect showing more survival with more helping (p.323). It may be that helpers actually improve fitness of reproductive-age meerkats and the young-but-not-juvenile. From: Doolan, S. P., D. W. McDonald (1997). "Breeding and Juvenile Survival Among Slender-Tailed Meerkats (Suricata suricatta) in the South-Western Kalahari: Ecological and Social Influences." Journal of Zoology 242: 309-327.

Tadpoles can respond to habitat dessication (pool drying) by accelerated metamorphosis as well as cannibalism. From: Newman, R. A. (1992). "Adaptive Plasticity in Amphibian Metamorphosis." Biosciences 42: 671-678.

Roughly 2m-diameter rafts of the kelp Macrocytis pyrifera observed in the Southern Ocean between South America and South Georgia island are small ecosystems composed of 100-200 kelp plants and, attached to them, 'colonies' of the mullosc Gaimardia trapesina; not only are adults of the mullosc found on the kelp, but young are as well, indicating that kelp rafts can serve as platforms sustaining mullosc populations on long-distance voyages. up to thousands of miles in distance.

Steller sea lions (Eumetopias jubatus) observed in Alaska's Prince William Sound feed exclusively on herring (Clupea pallasi) at night; they do not eat the much more abundant walleye pollock, which are roughly five times more abundant in these waters; in winter there is particular food source stress, but even then sea lions do not eat the pollock. However, pollock live at 100m or so depth (day and night), whereas herring schools occur closer to 15-35m deep at night. Groups of up to 50 stellers were observed swimming abreast, apparently herding the herring. Stellers can dive to 250m, but it is apparenly easier for them to herd the shallower-occurring herring than dive for the pollock. From: Thomas, G. L., and R.E. Thorne (2001). "Night-Time Predation by Steller Sea Lions." Nature 411: 1013.

Viruses are the most abundant and genetically diverse 'life forms' in the ocean; typically 10^7 viruses / ml, fewer with depth and distance from shore. They are most common where bacteria and chlorophyll are most abundant. Oceans contain perhaps 4x10^40 viruses; end-to-end they would reach 10m light years and they weigh = to 75m blue whales. These have genome sizes from 997bp to 1.1mbp (p.357) and are genetically extremely diverse. At the same time, some sequences are nearly identical at the nucleotide level in environments as distant as the Southern Ocean, Antarctica, and the Gulf of Mexico. New analysis shows that HGT has occurred between cyanobacteria and their viruses (p.358) such that "viruses capture genes of host origin and exhange them among viral progeny". On a daily basis, oceanic viruses kill 20-40% of all marine bacteria, and contribute to microbial mortality at a level similar to that of grazing by zooplankton. From Suttle, C. A. (2005). "Viruses in the Sea." Nature 437: 356-361.

Romanian tadpoles were observed to cannibalize conspecifics during a period when their pond was drying and crowded with tadpoles. This is an instance verifying other such instances of adaptive behavioral placticity as noted in Newman (1992). Kovacs, E. H. a. I. S. (2009). From: "Cannibalistic Behaviour of Epidalea (Bufo) viridis Tadpoles in and Urban Breeding Habitat." North-Western Journal of Zoology 5(1): 206-208.