Vol. 59, 2020
(update: 2020.07.06; 08.05)
Fossil and Modern Clam Shrimp (Branchiopoda: Spinicaudata, Laevicaudata)
Testing Weissman’s Lineage
Selection Model for the Maintenance of Sex: The Evolutionary Dynamics
of Clam Shrimp Reproduction over Geologic Time
I. Astrop1,*, Lisa Park Boush2, and Stephen C.
Forest Project, Blast Road, Brymbo, Wales, United Kingdom, LI11 5BT.
*Correspondence: E-mail: firstname.lastname@example.org (Astrop)
2Department of Geosciences, University of Connecticut,
Storrs, CT 06269-1045, USA. E-mail: email@example.com (Park
3Department of Biology, The University of Akron,
Akron, OH 44325-3908, USA. E-mail: firstname.lastname@example.org (Weeks)
(Received 11 June 2020 / Accepted 15
Special issue (articles 32-46) communicated by Thomas A. Hegna and D.
of the most perplexing questions within evolutionary biology is: “why
are there so many methods of reproduction?” Contemporary theories
assume that sexual reproduction should allow long term survival as
dispersal and recombination of genetic material provides a population
of organisms with the ability to adapt to environmental change. One of
the most frustrating aspects of studying the evolution of reproductive
systems is that we have not yet been able to utilize information locked
within the fossil record to assess breeding system evolution in deep
time. While the fossil record provides us with information on an
organism’s living environment, as well as some aspects of its ecology,
the preservation of biological interactions (reproduction, feeding,
symbiosis, communication) is exceedingly rare. Using both information
from extant taxa uncovered by a plethora of biological and ecological
studies and the rich representation of the Spinicaudata (Branchiopoda:
Crustacea) throughout the fossil record (from the Devonian to today),
we address two hypotheses of reproductive evolutionary theory: (1) that
unisexual species should be short lived and less speciose than their
outcrossing counterparts and (2) that androdioecy (mixtures of males
and hermaphrodites) is an unstable, transitionary system that should
not persist over long periods of time. We find no evidence of
all-unisexual spinicaudatan taxa (clam shrimp) in the fossil record,
but do find evidence of both androdioecious and dioecious clam shrimp.
We find that clades with many androdioecious species are less speciose
but persist longer than their mostly dioecious counterparts. These data
suggest that all-unisexual lineages likely do not persist long whereas
mixtures of unisexual and sexual breeding can persist for
evolutionarily long periods but tend to produce fewer species than
mostly sexual breeding.
Key words: Evolution of sex,
Sexual dimorphism, Morphometrics, Androdioecy, Chonchostraca.
Citation: Citation: Astrop TI, Park Boush
L, Weeks SC. 2020. Testing Weissman’s lineage selection model for the
maintenance of sex: the evolutionary dynamics of clam shrimp
reproduction over geologic time. Zool Stud 59:34. doi:10.6620/ZS.2020.59-34.