Advait Jukar & Laura Bradley
Behavioral phylogeny: occurence of a particular behavior in the evolutionary history of an organism.
What is the history of humpback whale migration? Investigations using the fossil record provide valuable information on the history of this organism. Humpback whales are a relatively ancient species, with fossil records dating from the late Pleistocene period (~130,000-10,000 B.C.E.) in Florida, the Pleistocene (1.8 million -10,000 B.C.E.) in Champlain Sea and the Holocene (10,000-present) in Japan (Deméré et al 2005). Mitochondrial DNA analyses have generated phylogentic trees for the humpback whale and related species (Figure 5A). It has been shown that the suborder to which humpbacks belong (Mysticeti) is diverging at a rate of 0.7 - 1.0% per million years (Figure 5B).
Figure 1. Mt DNA construction of phylogenetic tree of mysticetes. (A) Phylogenetic relationship of variable mtDNA control region sequences among mysticete whales, constructed using maximum likelihood (38) and parsimony (32) analyses. The tree is based on a 254-bp sequence of the control region beginning at position 29 in relation to the humpback whale sequence (Fig. 1). Sequences from more than one individual were used for the humpback (n = 3), fin (n = 2), and bowhead (n = 2) whales. The relative ranges of intraspecific variation are indicated by the depth of the branches in the cladogram. Transversions were weighted 10:1 over transitions in the data matrix. Percentages show agreement in a consensus of 500 bootstrap simulations of the data set using the branch and bound search option available in PAUP (34). (B) Divergence rate calibration for mysticete control regions. Sequence differences for control region data were calculated using equation 5 of Li et al. (39). Divergence dates (Mya) are minimum and maximum times from the fossil record for the genera or families compared, as described in text. The diagonal lines are the steepest and shallowest lines that pass through all data boxes and represent our best estimate of divergence rates.Mitrochondrial DNA (mt DNA) haplotypes obtained from humpback whales is a useful tool to construct phylogenic trees and indicate genetically similarity in distinct regions compared to other regions.
It is known that migratory routes have adapted over evolutionary time. For example, humpback whales have only begun migrating to the main Hawaiian islands in the 20th century, according to whaling reports (Herman 1979).
Evidence from magnetite particles
Humpback whales are believed to use internal magnetite particles to navigate during migration [see Mechanism]. This system was likely selected for to maximize the ability to detect geomagnetic field position. Selection acts to modify the average grain size of the magnetite crystals (Chang & Kirschvink 1989). Different organisms have evolved single-domain magnetite particles that are specific to the local environment of that animal (Figure 6).
Evidence from fossil records
Fossil records can also be used to decipher the mechanism by which humpback whales use the magnetic field to navigate. The fossil record may prove to be congruent with the Earth's regular magnetic reversal. Prior to the switch the magnetic field is absent, presenting a significant difficulty for whales to migrate and breed. Thus the fossil record should demonstrate that fewer whales survive during this period, though this has not yet been investigated (Kirschvink et al 1986). A confirmation of this hypothesis would elucidate the theory that humpback whales depend on the Earth's magnetic field for navigational cues during migration.
Through the use of multiple tools, including mitrochondrial DNA and fossil record analysis, as well as commercial whaling records, researchers believe it is likely that humpback whale migration is an ancient behavior.