Sunday, January 14, 2007


New Research Shows Larval Fish Use Smell to Return to Coral Reefs (Video)

There's No Scent Like Home - Press Release from the Marine Biological Laboratory, Woods Hole, Massachusetts: Tiny larval fish living among Australia's Great Barrier Reef spend the early weeks of their lives swept up in ocean currents that can disperse them far from their places of birth. Given such a life history, one might assume that fish populations would be genetically homogeneous within the dispersal area. Yet the diversity of reef fish species is high and individual reefs contain different fish populations. For such rich biodiversity to have evolved, some form of population isolation is required.

New research from MBL (Marine Biological Laboratory) Associate Scientist Gabriele Gerlach, MBL Adjunct Senior Scientist and Professor of Biology at Boston University Jelle Atema, and their colleagues shows that many fish species can discriminate odors in ocean currents and that some species use home reef scent to return to the reefs where they were born. The olfactory imprinting of natal reefs sheds light on how such a wide diversity of species arose. The homing behavior of reef fishes, the researchers contend, could support population isolation and genetic divergence that may ultimately lead to the formation of new species.

Gerlach, Atema, and their team will present the results of their research in next week's online Early Edition of The Proceedings of the National Academy of Sciences. The scientists studied fish populations in five neighboring reefs (all part of the Great Barrier Reef) where genetic mixing would be expected. They used a multidisciplinary approach including hydrodynamic modeling to describe prevailing ocean current distribution patterns among the reefs; genetic markers to track the relatedness of three species of fishes which live among the reefs; and olfactory choice tests using flumes to test the larvae's ability to smell the difference between water from the five reefs.

Their genetic analyses showed that while some fish species do disperse, other species return to their home reef. One species in particular, the cardinal fish (Ostorinchus doederleini), showed significant genetic differences among subpopulations even among reefs separated by as little as 3 km, which suggests strong homing. Using a flume aboard their boat, which exposed larvae to water samples collected from different reefs, the researchers tested if smell might be guiding factor leading the larvae home. The cardinal fish showed a preference for the water from their home reef over all other reefs, suggesting that olfactory cues could lead larvae back.

"This research shows that the spatial distribution of these aquatic organisms is far from being random despite long larval dispersal stages of several weeks," says Gerlach. "Apparently, these larvae - small as they are - use elaborate sensory mechanisms to orientate and find their way to appropriate habitats or express successful homing behavior to their natal spawning sites. This might play a major role in processes of population separation and, eventually, of speciation."

According to Gerlach, the results of this research could have important implications not only for the Great Barrier Reef, but for marine environments in general. "This information should be considered by marine managers as they designate the location and spacing of Marine Protected Areas," she says.

There are still many questions that remain to be answered. For example, Gerlach and Atema's results have not shown how the larvae learn the odor of their reef or how and when during development they use this information. Paper co-author Vanessa Miller-Sims is completing her Ph.D. thesis at Boston University with a focus on this subject. The scientists also do not know the chemical composition of the odor that the larvae use to recognize home. "It may be social odor from its own species or a peculiar mixture of compounds typical for one versus another reef, the way people's homes have typical odors," says Atema. "This chemical information will be important in terms of water quality and management. We are following up with research to obtain such knowledge."

Source: There's No Scent Like Home (January 8, 2007) Press Release (see Media Information link)


Based on the Proceedings of the National Academy of Sciences (PNAS) paper:

Gabriele Gerlach, Jelle Atema, Michael J. Kingsford, Kerry P. Black, and Vanessa Miller-Sims
Smelling home can prevent dispersal of reef fish larvae
Published online before print January 9, 2007, 10.1073/pnas.0606777104


Many marine fish and invertebrates show a dual life history where settled adults produce dispersing larvae. The planktonic nature of the early larval stages suggests a passive dispersal model where ocean currents would quickly cause panmixis over large spatial scales and prevent isolation of populations, a prerequisite for speciation. However, high biodiversity and species abundance in coral reefs contradict this panmixis hypothesis. Although ocean currents are a major force in larval dispersal, recent studies show far greater retention than predicted by advection models. We investigated the role of animal behavior in retention and homing of coral reef fish larvae resulting in two important discoveries: (i) Settling larvae are capable of olfactory discrimination and prefer the odor of their home reef, thereby demonstrating to us that nearby reefs smell different. (ii) Whereas one species showed panmixis as predicted from our advection model, another species showed significant genetic population substructure suggestive of strong homing. Thus, the smell of reefs could allow larvae to choose currents that return them to reefs in general and natal reefs in particular. As a consequence, reef populations can develop genetic differences that might lead to reproductive isolation.

Related MPEG video:

"This video shows an experimental compartment containing a damsel fish, Pomacentrus coelestis. Upon entry of foreign water from a nearby reef, the fish gets "nervous" and swims to the other side of the compartment which contains water from its home reef. The researchers repeated this experiment seven times with exactly the same result" (Running time: 18 mins) [Evolution]


See "Scientists have found a fossil that explains the history of the nose":

Our ancestors had two nostrils, one front and one back, but no opening on the palate or in the throat. They could smell, but not breathe with their nose. How did our nose evolve?

Per Ahlberg, Uppsala university, and Zhu Min, department of Vertebrate Paleontology in Beijing, China, has now found a fossil that explains the history of the nose.

Have you ever wondered, taking a deep breath of fresh autumn air and sensing how the smell of wet leaves tickles your nose, just how it came about that you can do so? We humans take it for granted that our nose forms a passage between the world around us and our windpipe, but this hasn't always been the case. We land-based vertebrates or "tetrapods" (mammals, birds, reptiles, and amphibians) originally descend from fish, and fish cant breathe through their nose. On the side of a fish's head there are two nostrils, one front and one back, that form the opening to a little sac containing the olfactory organs: water flows in through the front nostril and out through the back one, but there is no connection whatsoever to the throat. In other words, fish can smell with their nose, but not breathe.

The full article (dated 4-Nov-04) is available via this link (see under 'News Stories from November 2004') and is based on the journal Nature paper:

The origin of the internal nostril of tetrapods
Min Zhu1 and Per E. Ahlberg
Nature 432, 94-97 (4 November 2004) | doi: 10.1038/nature02843


The choana, a unique 'internal nostril' opening from the nasal sac into the roof of the mouth, is a key part of the tetrapod (land vertebrate) respiratory system. It was the first component of the tetrapod body plan to evolve, well before the origin of limbs, and is therefore crucial to our understanding of the beginning of the fish-tetrapod transition. However, there is no consensus on the origin of the choana despite decades of heated debate; some have claimed that it represents a palatally displaced external nostril but others have argued that this is implausible because it implies breaking and rejoining the maxillary-premaxillary dental arcade and the maxillary branch of nerve V2. The fossil record has not resolved the dispute, because the choana is fully developed in known tetrapod stem-group members. Here we present new material of Kenichthys, a 395-million-year-old fossil fish from China that provides direct evidence for the origin of the choana and establishes its homology: it is indeed a displaced posterior external nostril that, during a brief transitional stage illustrated by Kenichthys, separated the maxilla from the premaxilla.


Of related interest from National Geographic:

Moles, Shrews Can Smell Prey While Underwater

Two small, semiaquatic mammals can use their sense of smell even when underwater, according to a new study.

The finding stems from high-speed video that shows a star-nosed mole* rapidly blowing out bubbles of air and sucking them back in while foraging underwater.

The bizarre-looking rodent is already known as the world's fastest mammalian forager.

The mole has now displayed equal prowess as a lightning-fast underwater sniffer, blowing and inhaling air bubbles at a rate of five to ten times a second.

The bubbles make contact with a target, such as morsel of earthworm or fish, and apparently pick up the target's scent before being sucked back up the nose.

When you watch the video, "you're essentially seeing [the moles] sniffing underwater," said Kenneth Catania (lab), a biologist at Vanderbilt University in Nashville, Tennessee.

Continued at "Moles, Shrews Can Smell Prey While Underwater, Study Suggests"

Based on the journal Nature paper:

Olfaction: Underwater 'sniffing' by semi-aquatic mammals
Kenneth C. Catania
Nature 444, 1024-1025 (21 December 2006) | doi:10.1038/4441024a


Terrestrial species that forage underwater face challenges because their body parts and senses are adapted for land - for example, it is widely held that mammals cannot use olfaction underwater because it is impossible for them to inspire air (sniff) to convey odorants to the olfactory epithelium. Here I describe a mechanism for underwater sniffing used by the semi-aquatic star-nosed mole (Condylura cristata) and water shrew (Sorex palustris). While underwater, both species exhale air bubbles onto objects or scent trails and then re-inspire the bubbles to carry the smell back through the nose. This newly described behaviour provides a mechanism for mammalian olfaction underwater.

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