during their whole life cycle (Muro-Cruz et al. 2002).
The total production of eggs of O. longicaudis over the
course of its life cycle (22 eggs female−1) was low compared
to other Chydoridae, since it has a longer embryonic development
time, and a later primipara. Similar production of
eggs has been observed by Santos-Wisniewski et al. (2006)
to C. pubescens (22.3 eggs female−1), by Murugan and Job
(1982) to L. acanthocercoides (20 eggs female−1), and in
Euryalona orientalis (20 eggs female−1) by Venkataraman
(1990), and longevity of these species ranged from 23 to
25 days. Longer-lived species such as A. excisa (73.4 days)
(Sharma and Sharma 1998) and Leydigia ciliata (46 days)
(Venkataraman 1990) produced 46 and 50 eggs female−1 in
their whole life cycle, respectively. A. excisa had a shorter
embryonic development time, and L. ciliate, grown at a
higher temperature by increasing the metabolism of organisms,
probably lead to a shorter embryonic development.
O. longicaudis stopped producing eggs near the end of its
life cycle, contributing to lower total fertility.
The mean size of neonate of O. longicaudis was about
50% less than the maximum size of adults. Smaller species
tend to produce offspring with a hatching length closer to
their adult size than the larger species (Lynch 1980).
DNA barcode of O. longicaudis
This study established the first barcode region of COI
for the Cladocera species O. longicaudis isolated in Brazil.
The percentage found for A-T (64.4%) is consistent with
the data range previously described for the 60% A-T percentage
for COI of Chydoridae (Sacherová and Hebert
2003; Belyaeva and Taylor 2009).
One value to consider is the 7.2% and 7.0% value of genetic
divergence among O. longicaudis from Brazil and the
other seven isolates from Mexico. For the Branchiopoda
group, a genetic divergence of 3% in the COI sequence is
considered a parameter for distinguishing species at the
molecular level. From 3% to 5%, the species is considered
provisional, and its taxonomic status should be confirmed.
Above 5%, the specimens are considered different species
(Jeffery et al. 2011). From this view, a genetic divergence
of around 7% found between our O. longicaudis and the
specimens from Mexico should be sufficient to classify
them as different species. In order to confirm this and create
a new species name, it will be necessary to perform
additional morphological detailed studies combined with
other molecular markers. However, among all O. longicaudis
from Mexico, the genetic divergence ranged from 0 to
0.2% (Table 2), emphasizing that they represent the same
species names.
COI analysis represents an interesting approach to new
studies of taxonomy and species recognition of Brazilian
isolates as new species, including cryptic species. Also,
COI can be used to analyze a zooplankton community
to estimate species richness of an entire zooplankton
community as already proposed by Machida et al. (2009)
and for further phylogeographic studies and gene flow
for subpopulations as recently described for copepods
(Young et al. 2014). Also, our results using COI markers
strengthen the continental endemism idea for Cladocera
(Forró et al. 2008; Belyaeva and Taylor 2009) and the
monopolization hypothesis for aquatic organisms such
as cladocerans (De Meester et al. 2002).
Conclusions
The embryonic and post-embryonic development times
of O. longicaudis were higher than those of the other
species of the same family, which contributed to lower
total egg production throughout its life cycle.
For the DNA barcoding, the roughly 7% genetic divergence
found between our O. longicaudis and the specimens
from Mexico highlights the possibility of a cryptic speciation
for this species and the urgent necessity to clarify the
taxonomic position.