As is the case of all beaked and bottlenose whales, exactly where Berardius fits into Ziphiidae is currently not clear. Morphological analysis of Cetacea by Geisler and Sanders 2003 placed Berardius and Mesoplodon into a clade - nobody else seems to have gotten this result and it is worth noting that Hyperoodon and Indopacetus were not included. Lambert et al. 2005 studied the morphology of extinct and extant ziphiids and placed Berardius in a basal position and possibly in a clade with Tasmacetus on the basis of one apomorphy (nasals wider than frontals on the vertex). Bianucci et al. 2007 defined the subfamily Berardiinae as an outgroup to other ziphiids mostly on the basis of symplesiomorphies such as a low vertex, a narrow and thin premaxillary crest and a supraoccipital lower than frontals; the only apomorphy shared by all the taxa* was a nodular protuberance formed by either the interparietals or frontals on the vertex. Dalebout et al. 2004 noted previous morphological and molecular studies that placed Berardius as the basal-most species and used it to root their tree but molecular studies of Cetacea by May-Collado and Agnarsson 2006 did not place it basally and noted that positions in the family are unresolved.
*Other members of the subfamily include the middle Miocene Archaeziphius from Belgium (Lambert and Louwye 2006), Microberardius from South Africa (Bianucci et al. 2007), an indeterminate species (Berardiinae indet. - Bianucci et al. 2007) from the same locale and a possible member of Berardius from Japan. Archaeziphius was only estimated at 3.5-4 m and Microberardius seemed similarly sized.
The osteological characters and genetic analyses don't really convey how much of a derived oddball Berardius is. Male ziphiids of other species have on pair of enlarged teeth (even many-toothed Tasmacetus and M. grayi) but Berardius* has both an apical and sub-apical pair on the mandible (Bianucci et al. 2007). The fossil genera did not have mandibles so we can't tell if they had the extra teeth - and I'll admit that I'm not quite sure what the smaller posterior pair do. Enlarged teeth in ziphiids are used in intraspecific combat and create parallel scars (except in M. ginkgodens?) which the cetacean delays pigmenting so they can accumulate and give a signal of "quality" so unnecessary aggressive behavior between unevenly matched males can be avoided (MacLeod 2003). If attaining scars as a status symbol seems odd, it should be pointed out that a Homo sapiens fad at Heidelberg University involved fencing duels for the sole purpose of getting scars. Back in the day when Berardius was still quite mysterious, Pike 1953 noted scars on both males and females of the species - but for some reason thought that neither had erupted teeth and the most parsimonious explanation was that the long parallel scars were caused by squid beaks (not squid hooks?). That aside, it is now established that both genders of both species have "battle teeth" (to use Connor et al. 1998's terminology) when mature. MacLeod et al. 2003 suggest that the teeth may be important in social interactions for females and could indicate dominance, but it remains to be studies how much scarring exactly occurs in females relative to males. MacLeod et al. also speculate that females may retain teeth due to "ontological constraint" - but Risso's dolphin and sperm whales were also being mentioned in the paragraph and the statement was probably directed more towards them since other ziphiids showed no signs of such a restraint.
*Other members of the subfamily include the middle Miocene Archaeziphius from Belgium (Lambert and Louwye 2006), Microberardius from South Africa (Bianucci et al. 2007), an indeterminate species (Berardiinae indet. - Bianucci et al. 2007) from the same locale and a possible member of Berardius from Japan. Archaeziphius was only estimated at 3.5-4 m and Microberardius seemed similarly sized.
The osteological characters and genetic analyses don't really convey how much of a derived oddball Berardius is. Male ziphiids of other species have on pair of enlarged teeth (even many-toothed Tasmacetus and M. grayi) but Berardius* has both an apical and sub-apical pair on the mandible (Bianucci et al. 2007). The fossil genera did not have mandibles so we can't tell if they had the extra teeth - and I'll admit that I'm not quite sure what the smaller posterior pair do. Enlarged teeth in ziphiids are used in intraspecific combat and create parallel scars (except in M. ginkgodens?) which the cetacean delays pigmenting so they can accumulate and give a signal of "quality" so unnecessary aggressive behavior between unevenly matched males can be avoided (MacLeod 2003). If attaining scars as a status symbol seems odd, it should be pointed out that a Homo sapiens fad at Heidelberg University involved fencing duels for the sole purpose of getting scars. Back in the day when Berardius was still quite mysterious, Pike 1953 noted scars on both males and females of the species - but for some reason thought that neither had erupted teeth and the most parsimonious explanation was that the long parallel scars were caused by squid beaks (not squid hooks?). That aside, it is now established that both genders of both species have "battle teeth" (to use Connor et al. 1998's terminology) when mature. MacLeod et al. 2003 suggest that the teeth may be important in social interactions for females and could indicate dominance, but it remains to be studies how much scarring exactly occurs in females relative to males. MacLeod et al. also speculate that females may retain teeth due to "ontological constraint" - but Risso's dolphin and sperm whales were also being mentioned in the paragraph and the statement was probably directed more towards them since other ziphiids showed no signs of such a restraint.
*Heuvelmans claims that B. arnuxii has "teeth which no mammalogist would have believed in had they been described by a layman, for they are embedded in cartilaginous sacs, and it seems that they can be erected at will". Heuvelmans does not make clear whom he is citing and Mead 2007 notes that morphology and osteology in B. bairdii and B. arnuxii are similar enough to possible be considered conspecific.
The social system of Berardius bairdii is described as "alien" to those more familiar with large terrestrial mammals (Connor et al. 1998). Connor et al. summarized a paper by Kasuya and Brownell using data from Japanese whalers (which I can't access) which suggest that adult males are much more common, mature 4 years earlier and live up to 30 years longer. To them, this indicates that the male plays a large role in parental care and/or for the young of a close female relative. The former scenario makes evolution sense because you always know that a sister and her offspring are related to you, but you can never be sure about "your own" kid. What doesn't make sense is how exactly female mortality fits into this scenario - unless they're the ones doing most of the fighting. It seems that all female ziphiids are larger than males judging by record sizes (Reeves et al. 2002) despite the aggressive intraspecific behavior of males and the fact that the males have a coloration pattern whereas females are nondescript. Kinda reminds me of frigatebirds. Berardius still retains larger females, but these ones have tusks and a similarly nondescript coloration (as far as I can tell) - the significance of which is totally beyond me. Reeves et al. 2002 noted that B. bairdii remains have been found in Orcas (Orcinus orca) and scars from Orcas have been found on B. bairdii as well. Could the enlarged teeth on female B. bairdii be used as a defense mechanism against orcas? More data would be nice, but again, it'll probably come from "scientific" whaling...
That's right, a species of ziphiid was and is still being hunted. B. bairdii is the largest ziphiid at 10 m average (MacLeod 2005)* and is apparently more approachable by boat than other species (Barlowe et al. 2006)** which is not a good trait for a cetacean occurring off the coast of Japan. It is likely that the species is below historical levels (Barlowe et al. 2006) and the Japanese killed 4000 between 1948 and 1986 with a peak of 300 per year in 1952 (Reeves et al. 2002). The IUCN considers this species as "Lower risk conservation dependent" (and not data deficient!) but suggests that more surveys are needed to make sure the Japanese quota of 62 animals per annum isn't depleting any local populations. Barlowe et al. 2006 note that in some "hot spots" the density of B. bairdii off Japan can reach 40-68 animals per 1000 Kilometers2 - but in other areas surveyed in the Pacific it ranged from 0.1 to 1.2. It still appears that overall abundance is somewhere in the thousands and being a species with a multi-tonne average weight***, Berardius has a significant biomass and is likely important ecologically.
* Lengths of 22 individuals indicated an average of 10.5 m (~34') for females and 9.6 m (~31'). MacLeod did not have sufficient evidence to give an average for B. arnuxii and from the 7 individuals measured the longest was 9.3 m (~30') as compared to the longest B. bairdii which measured 11 m (36'). Morisaka and Connor 2007 cite something I cannot locate which gives a length of 8.61 (~28') for the average B. arnuxii and this seems proportionally correct. Wikipedia claims that sightings of B. arnuxii included 12 m animals, but it is Wikipedia. Such lengths are probably unusual even for B. bairdii.
** Reeves et al. 2002 and Minamikawa et al. 2007 say that they are shy and difficult to approach. The latter study approached 35 of 63 pods sighted and were able to approach 3 pods within 30 m and 10 within 100 m. Maybe the species is more approachable relative to other ziphiids since it is so much more conspicuous.
***Minamikawa et al. 2007 and others apparently estimate the weight of these ziphiids by assuming 1 m of body length equals 1 tonne. They're going to need to be re-estimated.
MacLeod et al. 2003 commented that while a lot of B. bairdii specimens have been taken, information on stomach contents was rather limited. Previous studies cited by them suggested that B. bairdii migrated north in spring to feed on deep water fish and squid were primarily consumed while migrating south in fall. Ohizumi et al. 2003 studies diet more in depth and determined that B. bairdii was not dependent on vertical migration in deep water fish (i.e. upwards at night and vice versa) since the mass of consumed prey peaked during the day (but stomachs were empty in some). Data logging by Minamikawa et al. 2007 indicated that there were both dives that followed the bottom topography in very deep water (>1000 m) and others that did not appear to reach the bottom. Ohizumi et al. 2003 recorded mesopelagic squid in the stomach contents but Minamikawa et al. could not find indication of a feeding event (a zigzag pattern) and further acoustic study needs to be done. While most sources state that squid are the preferred prey of ziphiids, Ohizumi et al. 2003 suggest that desmeral fish (particularly hake and rat-tail) are important in their diet and may possibly be the reason for their migration.
That's right, a species of ziphiid was and is still being hunted. B. bairdii is the largest ziphiid at 10 m average (MacLeod 2005)* and is apparently more approachable by boat than other species (Barlowe et al. 2006)** which is not a good trait for a cetacean occurring off the coast of Japan. It is likely that the species is below historical levels (Barlowe et al. 2006) and the Japanese killed 4000 between 1948 and 1986 with a peak of 300 per year in 1952 (Reeves et al. 2002). The IUCN considers this species as "Lower risk conservation dependent" (and not data deficient!) but suggests that more surveys are needed to make sure the Japanese quota of 62 animals per annum isn't depleting any local populations. Barlowe et al. 2006 note that in some "hot spots" the density of B. bairdii off Japan can reach 40-68 animals per 1000 Kilometers2 - but in other areas surveyed in the Pacific it ranged from 0.1 to 1.2. It still appears that overall abundance is somewhere in the thousands and being a species with a multi-tonne average weight***, Berardius has a significant biomass and is likely important ecologically.
* Lengths of 22 individuals indicated an average of 10.5 m (~34') for females and 9.6 m (~31'). MacLeod did not have sufficient evidence to give an average for B. arnuxii and from the 7 individuals measured the longest was 9.3 m (~30') as compared to the longest B. bairdii which measured 11 m (36'). Morisaka and Connor 2007 cite something I cannot locate which gives a length of 8.61 (~28') for the average B. arnuxii and this seems proportionally correct. Wikipedia claims that sightings of B. arnuxii included 12 m animals, but it is Wikipedia. Such lengths are probably unusual even for B. bairdii.
** Reeves et al. 2002 and Minamikawa et al. 2007 say that they are shy and difficult to approach. The latter study approached 35 of 63 pods sighted and were able to approach 3 pods within 30 m and 10 within 100 m. Maybe the species is more approachable relative to other ziphiids since it is so much more conspicuous.
***Minamikawa et al. 2007 and others apparently estimate the weight of these ziphiids by assuming 1 m of body length equals 1 tonne. They're going to need to be re-estimated.
MacLeod et al. 2003 commented that while a lot of B. bairdii specimens have been taken, information on stomach contents was rather limited. Previous studies cited by them suggested that B. bairdii migrated north in spring to feed on deep water fish and squid were primarily consumed while migrating south in fall. Ohizumi et al. 2003 studies diet more in depth and determined that B. bairdii was not dependent on vertical migration in deep water fish (i.e. upwards at night and vice versa) since the mass of consumed prey peaked during the day (but stomachs were empty in some). Data logging by Minamikawa et al. 2007 indicated that there were both dives that followed the bottom topography in very deep water (>1000 m) and others that did not appear to reach the bottom. Ohizumi et al. 2003 recorded mesopelagic squid in the stomach contents but Minamikawa et al. could not find indication of a feeding event (a zigzag pattern) and further acoustic study needs to be done. While most sources state that squid are the preferred prey of ziphiids, Ohizumi et al. 2003 suggest that desmeral fish (particularly hake and rat-tail) are important in their diet and may possibly be the reason for their migration.
Tying in with the previously mentioned notion that Berardius is an oddball, Mead 2007 first described the apomorphy of a derived stomach anatomy in B. bairdii. The main chamber of the stomach has a valvular closure which divides it into another compartment. After a complex of connecting chambers is a pyloric stomach of similar size to the main stomach which communicates freely with a much smaller pyloric stomach chamber. Mead noted that functional anatomy of multiple stomachs even in familiar ungulates (cows, sheep) is not yet conclusive, so how exactly this relates to diet cannot yet be known. Interestingly, he predicts that the stomach anatomy of B. arnuxii will be very similar...
So what exactly should the status of Berardius species be? Judging by distribution data (in MacLeod et al. 2006) it seems that B. bairdii and B. arnuxii are separated by 60-70 degrees of latitude so they can be considered species by the biological species concept. Bianucci et al. 2007 note that a bone interpreted as the interparietal is in a plesiomorphic (?) position in B. arnuxii, but apparently not always. Aside from the reported size difference between species (maybe - this isn't really a character anyways) some very early authorities reported a difference in body length relative to head length, but this has been discounted as variation since Slipp and Wilke 1953. Mead 2007 simply states that the osteology and morphology between species is extremely similar and externally it is stated that the species are indistinguishable (Reeves et al. 2002). Molecular analysis by Dalebout et al. 1998 revealed that the interspecific variation in Berardius spp. is somewhat less than variation within Hyperoodon planifrons - and presumably variation between H. planifrons and H. ampullatus (the other antitropical giant whales) is a whole lot greater (Mead mentions that they are in different subgenera). Regardless of what species placement may be in the future, for conservation purposes they should most certainly be treated as separate entities. I couldn't help but be a little curious that the IUCN gave the species the same conservation status - is B. arnuxii really not data deficient?
Anyways, more ziphiids coming at some point. I'm not sure which ones.
Anyways, more ziphiids coming at some point. I'm not sure which ones.
References:
Barlowe, Jay et al. 2006. Abundance and densities of beaked and bottlenose whales (family Ziphiidae). J. Cetacean Res. Manage. 7(3):263–270
Bianucci, Giovanni et al. 2007. A high diversity in fossil beaked whales (Mammalia, Odontoceti, Ziphiidae) recovered by trawling from the sea floor off South Africa. A high diversity in fossil beaked whales (Mammalia, Odontoceti, Ziphiidae) recovered by trawling from the sea floor off South Africa. Geodiversitas 29 (4) : 561-618.
Connor, Richard C. et al. 1998. Social evolution in toothed whales. TREE vol. 13, no. 6.
Dalebout, Merel L. et al. 2004. A Comprehensive and Validated Molecular Taxonomy of Beaked
Whales, Family Ziphiidae. Journal of Heredity 95(6): 459–473. Available
Dalebout, Merel L. et al. 1998. Molecular genetic identification of southern hemisphere beaked whales (Cetacea: Ziphiidae). Molecular ecology 7, 687-694.
Geisler, Jonathan H. and Sanders, Albert E. 2003. Morphological Evidence for the Phylogeny of Cetacea. Journal of Mammalian Evolution, Vol. 10, Nos. 1/2,
Heuvelmans, Bernard. In the Wake of the Sea-Serpents. Hill and Wang, New York, 1968.
Lambert, Oliver and Louwye, Stephen. 2006. Archaeoziphius microglenoideus, a new primitive beaked whale (Mammalia, Cetacea, Odontoceti) from the middle Miocene of Belgium. Journal of Vertebrate Paleontology 26(1):182–191
MacLeod, Colin D et al. 2006. Known and inferred distributions of beaked whale species
(Cetacea: Ziphiidae). J. Cetacean Res. Manage. 7(3):271–286,
MacLeod, Colin D. 2005. Niche Partitioning, Distribution And Competition In North Atlantic Beaked Whales. Doctoral Thesis. Available
MacLeod, Colin D. 2003. Intraspecific scarring in odontocete cetaceans: an indicator of
male `quality' in aggressive social interactions? J. Zool., Lond., (244) 71-77
May-Collado, Laura and Agnarsson, Ingi. 2006. Cytochrome b and Bayesian inference of whale phylogeny. Molecular Phylogenetics and Evolution 38, 344–354
Mead, James G. 2007. Stomach Anatomy and Use in Defining Systemic Relationships of the Cetacean Family Ziphiidae (Beaked Whales). The Anatomical Record 290:581–595
Minamikawa, Shingo et al. 2007. Diving behaviour of a Baird’s beaked whale, Berardius bairdii,
in the slope water region of the western North Pacific: first dive records using a data logger. Fish. Oceanogr. 16:6, 573–577,
Morisaka, T and Connor, R. C. 2007. Predation by killer whales (Orcinus orca) and the evolution of whistle loss and narrow-band high frequency clicks in odontocetes. Journal of Evolutionary Biology. Vol. 20, No. 4, pp. 1439-1458.
Ohizumi, Hiroshi et al. 2003. Feeding habits of Baird’s beaked whale Berardius bairdii, in the western North Pacific and Sea of Okhotsk off Japan. Fisheries Science 69: 11-20
Pike, Gordon S. 1953. Two records of Berardius bairdi from the coast of British Columbia. Journal of Mammalogy. Vol. 34, No. 1, pp. 98-104.
Reeves, Randall R. et al. 2002. National Audubon Society Guide to Marine Mammals, Alfred A. Knopf, New York.
Slipp, T. W. and Wilke, Ford. 1953. The Beaked Whale Berardius on the Washington Coast. Journal of Mammalogy, Vol. 34, No. 1, pp. 105-113
No comments:
Post a Comment