Antitropical distribution explained

Antitropical (alternatives include biantitropical or amphitropical) distribution is a type of disjunct distribution where a species or clade exists at comparable latitudes across the equator but not in the tropics. For example, a species may be found north of the Tropic of Cancer and south of the Tropic of Capricorn, but not in between.^[1] With increasing time since dispersal, the disjunct populations may be the same variety, species, or clade.^[2] How the life forms distribute themselves to the opposite hemisphere when they can't normally survive in the middle depends on the species; plants may have their seed spread through wind, animal, or other methods and then germinate upon reaching the appropriate climate, while sea life may be able to travel through the tropical regions in a larval state or by going through deep ocean currents with much colder temperatures than on the surface. For the American amphitropical distribution, dispersal has been generally agreed to be more likely than vicariance from a previous distribution including the tropics in North and South America.

Known cases

Plants

• Phacelia crenulata – scorpionweed
• Bowlesia incana – American Bowlesia
• Osmorhiza berteroi and Osmorhiza depauperata – sweet cecily species.
• Ruppia megacarpa^[3]
• Solenogyne^[4]
• For a list of American amphitropically distributed plants (237 vascular plants), see the tables in the open access paper Simpson et al. 2017 or their working group on figshare^[5]

Animals

• Scylla serrata – mud crab
• Freshwater crayfish
• Ground beetle genus Bembidion

Bryophytes and lichens

• Tetraplodon fuegianus^[6] - dung moss

See also

• Rapoport's rule

Notes and References

1. Raven. Peter H.. 1963. Amphitropical Relationships in the Floras of North and South America. The Quarterly Review of Biology. en. 38. 2. 151–177. 10.1086/403797. 85310607 . 0033-5770.
2. Simpson. Michael G.. Johnson. Leigh A.. Villaverde. Tamara. Guilliams. C. Matt. 2017. American amphitropical disjuncts: Perspectives from vascular plant analyses and prospects for future research. American Journal of Botany. en. 104. 11. 1600–1650. 10.3732/ajb.1700308. 0002-9122. free. 10261/168338. free.
3. Ito, Y., T. Ohi-Toma, J. Murata and Nr. Tanaka (2010) Hybridization and polyploidy of an aquatic plant, Ruppia (Ruppiaceae), inferred from plastid and nuclear DNA phylogenies. American Journal of Botany 97: 1156-1167
4. Nakamura, K., T. Denda, G. Kokubugata, P.I. Forster, G. Wilson, C.-I Peng, M. Yokota (2012) Molecular phylogeography reveals an antitropical distribution and local diversification of Solenogyne (Asteraceae) in the Ryukyu Archipelago of Japan and Australia. Biological Journal of the Linnean Society 105: 197-217
5. Web site: American Amphitropical Disjunction Working Group. figshare.com. 2019-02-23.
6. Lewis. Lily R.. Biersma. Elisabeth M.. Carey. Sarah B.. Holsinger. Kent. McDaniel. Stuart F.. Rozzi. Ricardo. Goffinet. Bernard. 2017. Resolving the northern hemisphere source region for the long-distance dispersal event that gave rise to the South American endemic dung mossTetraplodon fuegianus. American Journal of Botany. 104. 11. 1651–1659. 10.3732/ajb.1700144. 0002-9122. free.