Cranial variation in allactagine jerboas(Allactaginae,Dipodidae, Rodentia): a geometric morphometric study

Allactaginae is a subfamily of dipodids consisting of four-and five-toed jerboas(Allactaga, Allactodipus,Orientallactaga, Pygeretmus, Scarturus) found in open habitats of Asia and North Africa. Recent molecular phylogenies have upended our understanding of this group's systematics across taxonomic scales. Here, I used cranial geometric morphometrics to examine variation across 219 specimens of 14 allactagine species(Allactaga major, A. severtzovi, Orientallactaga balikunica, O.bullata, O. sibirica, Pygeretmus platyurus, P. pumilio,P. shitkovi, Scarturus aralychensis, S. euphraticus,S. hotsoni, S. indicus, S. tetradactylus, S. williamsi)in light of their revised taxonomy. Results showed no significant sexual size or shape dimorphism. Species significantly differed in cranial size and shape both overall and as species pairs. Species identity had a strong effect on both cranial size and shape. Only a small part of cranial shape variation was allometric,with no evidence of unique species allometries, and most specimens fit closely to the common allometric regression vector. Allactaga was the largest,followed by Orientallactaga, Scarturus, and finally Pygeretmus. Principal component 1(PC1) separated O. bullata+O. balikunica+S. hotsoni(with inflated bullae along with reduced zygomatic arches and rostra) from A. major+A. severtzovi+O. sibirica(with converse patterns), while PC2 differentiated Orientallactaga(with enlarged cranial bases and rostra along with reduced zygomatic arches and foramina magna) from Scarturus+Pygeretmus(with the opposite patterns). Clustering based on the unweighted pair group method with arithmetic mean(UPGMA) contained the four genera, but S. hotsoni clustered with O. bullata+O. balikunica and O.sibirica clustered with A. major+A. severtzovi, likely due to convergence and allometry, respectively.

Genomic insights into adaptation to bipedal saltation and desert-like habitats of jerboas

Jerboas is a lineage of small rodents displaying atypical mouse-like morphology with elongated strong hindlimbs and short forelimbs.They have evolved obligate bipedal saltation and acute senses,and been well-adapted to vast desert-like habitats.Using a newly sequenced chromosome-scale genome of the Mongolian five-toed jerboa(Orientallactaga sibirica),our comparative genomic analyses and in vitro functional assays showed that the genetic innovations in both protein-coding and non-coding regions played an important role in jerboa morphological and physiological adaptation.Jerboa-specific amino acid substitutions,and segment insertions/deletions(indels)in conserved non-coding elements(CNEs)were found in components of proteoglycan biosynthesis pathway(XYLT1 and CHSY1),which plays an important role in limb development.Meanwhile,we found specific evolutionary changes functionally associated with energy or water metabolism(e.g.,specific amino acid substitutions in ND5 and indels in CNEs physically near ROR2)and senses(e.g.,expansion of vomeronasal receptors and the FAM136A gene family)in jerboas.Further dual-luciferase reporter assay verified that some of the CNEs with jerboa-specific segment indels exerted a significantly different influence on luciferase activity,suggesting changes in their regulatory function in jerboas.Our results revealed the potential molecular mechanisms underlying jerboa adaptation since the divergence from the Eocene-Oligocene transition,and provided more resources and new insights to enhance our understanding of the molecular basis underlying the phenotypic diversity and the environmental adaptation of mammals.

Cranial differences in three-toed jerboas(Dipodinae,Dipodidae,Rodentia)according to recent taxonomic revisions

Recent phylogenetic studies amended the taxonomy of three-toed jerboas(subfamily Dipodinae),including raising subspecies to full species.Here,we use geometric morphometrics to compare scaled-shape differences in dipodine crania while considering their revised taxonomy.We sampled Dipus deasyi,D.sagitta halli,D.s.sowerbyi,Jaculus blanfordi blanfordi,J.hirtipes,J.jaculus,J.loftusi,J.orientalis gerboa,J.o.mauritanicus,and Stylodipus andrewsi.Crania were not sexually dimorphic.Common allometry explained some of the shape variation,for example,reduced braincases in larger specimens.Most operational taxonomic unit pairs differed in both size and shape.Dipus and Stylodipus clustered together based on their cranial shape.Jaculus differed from the aforementioned genera by its larger tympanic bulla,broader braincase,larger infraorbital foramen,along with reduced molars and rostra.Jaculus orientalis differed from other Jaculus by its broader face versus reduced cranial vault.Jaculus blanfordi(subgenus Haltomys)resembles members of the subgenus Jaculus more than its consubgener(J.orientalis).Jaculus loftusi,previously considered a synonym of J.jaculus,clearly differed from the latter by its shorter rostrum,smaller infraorbital foramen,and more caudolaterally expanded tympanic bulla.Jaculus hirtipes,another recent synonym of J.jaculus,resembled J.blanfordi more in scaled cranial shape than it did J.jaculus.Dipus sagitta halli and D.s.sowerbyi were indistinguishable,but they clearly differed from D.deasyi(recently raised to full species)with the latter having a larger molar row,more inflated tympanic bulla,and shorter,slenderer rostrum.Ecological explanations for detected cranial shape differences are considered,including diet and habitat(particularly substrate).

Allozyme Polymorphism and Genetic Differentiation Among Populations of Jaculus jaculus and J. orientalis (Rodentia: Dipodidae) in Tunisia

Genetic variability and divergence among natural populations of Jaculus jaculus and J. orientalis in Tunisia were examined by electrophoretic analysis of 16 enzymatic proteins encoded by 23 genetic loci. Low levels of genetic variability were found among populations of both species in comparison to those of other rodent and mammal species of which data are available. In J. jaculus populations, the mean level of observed heterozygosity （Hobs） ranged from 0.08 to 0.19, while the mean percentage of polymorphic loci （P） ranged from 26.2% to 45.2% and the mean number of alleles per locus （A） ranged from 1.1 to 1.4. Nevertheless, the mean values were 0.10 to 0.15, 29.3% to 44.1% and 1.1 to 1.7, respectively, for J. orientalis. In addition, populations of the two species have revealed a lower degree of genetic differentiation （Fst=0.0017 for J. jaculus and 0.0019 for J. orientalis）. Moreover, Fst was 0.607, P〈0.05 between populations of the two species, indicating that they were highly genetically diverged from each other. The present data assures the previous results on the validity of the present taxonomic situation of the two species and emphasis on the effect of geographic factors （environments type and bioclimatic stages） on the genetic structure of both species.