Discussion
Characteristics of
Tenebrionoidea mtgenomes
These 90 mtgenomes investigated in
the present study in the superfamily Tenebrionoidea have a length
variation from 14 777 bp to 16 861 bp, and the length variation mainly
stems from CR, intergenic overlap and spacers, which is consistent with
earlier reports in Tenebrionoids
(Burger et al. , 2003). The
nucleotide composition for all species exhibits obvious AT bias with
high A+T content, similar as earlier reports in Tenebrionoids
(Jie et al. , 2016). All
tRNA genes can form a complete clover secondary structure, except fortRNA -Ser (AGN) that lacks the DHU arm, which seem to be a
common feature of Tenebrionoidea
(Zhang et al. , 2016; Songet al. , 2018). There are
some
rearrangement events in some
species of the family Mordellidae, Lagriidae and Pyrochroidae. The
shuffling of the trnR and trnN genes
(trnA-trnR-trnN-trnS-trnE-trnF gene cluster) is found in all
specials in the family Mordellidae;
the translocation of thetrnD and ATP8 genes is found in the A. rugipennisof Lagriidae for the first time; the shuffling of the trnC andtrnW genes (trnW-trnC-trnY gene cluster) is found in
Pyrochroidae and Lagriidae. These gene rearrangement may be produced by
abnormal priming of mitochondrial replication by a tRNA molecule or
tandem duplications, which can provide an important reference for
Tenebrionoidea phylogeny inference (Boore & Brown, 1998; Boore et
al. , 1998; Timmermans & Vogler, 2012; Cameron, 2014). The ATN and TTG
are mainly used as the start codon, and TAA and TAG as the stop codon
for the 13 PCGs, which is similar as other mtgenome sequences in
Tenebrionoidea (Du et al. ,
2017). The Ka/Ks ratio is lower than one for all PCGs, which is
consistent with earlier studies in Tenebrionoidea. The COX1 gene
has experienced strong evolutionary pressure in order to maintain its
own functional requirements, whereas ATP8 has experienced weak
evolutionary pressures with allowing more mutations to accumulate in the
mtgenome (Ou et al. , 2016;
Bai et al. , 2018).
Overview
of phylogenetic relationships
A total of 16 families are
included in the phylogenetics and evolution analysis in the
Tenebrionoidea, in which there are 10 families with at least two
representative species included. The family
Ciidae seems to be earliest
derived in these families, followed
Mordellidae + Ripiphoridae,
and Aderidae + “Meloidae clade”
+ “Tenebrionidae clade”. Ciidae
was historily placed in the Cucujoidea (Crowson, 1955) and then to the
superfamily Tenebrionoidea mainly based on characteristics of the
aedeagus and the larval abdomen (Crowson, 1960).
It was proposed to be a monophyly
based on 18S and COX1 genes using ML and BI methods, and
demonstrated to be a either sister to Nitidulidae based on the reduced
sample or at the base of the cucujoid-tenebrionoid assemblage based on
the entire sample (Buder et al. , 2008). It was considered
basal tenebrionoids based on 516
adult and larval morphological characteristics from 359 beetle taxa
(Lawrence et al ., 2011). The present study also suggests the
family to be the basal tenebrionoids, but further investigation is
necessary to elucidate its place with the inclusion of more species.
Mordellidae + Ripiphoridae,
Mordellidae and Ripiphoridae are all proposed to be monophyletic, and
the two families demonstrate to be sister groups each other in the
present study. The Mordellidae + Ripiphoridae was also proposed
monophyletic in earlier molecular phylogeny inference based on five
nuclear and mitochondrial genes with 300 genera in Tenebrionoidea using
ML (Gunter et al. , 2014). The Mordellidae was also proposed to be
monophyletic in the study based on four molecular genes (18SrRNA, 28S rRNA, rrnL and COX1 ) with 128 species in
Tenebrionoidea using ML (Batelka et al. , 2016). The Ripiphoridae
was proposed to be monophyletic from a molecular phylogenetic analysis
based on eight nuclear genes with 367 species in Tenebrionoidea using
Bayesian method (Mckenna et al. , 2015). However, it was proposed
to be paraphyletic in the molecular phylogenetic study based on
four mitochondrial and four
nuclear gene fragments across 404 taxa (including 250 tenebrionid
species) using ML (Kergoat et al. , 2014a), which suggests that
the monophyletic status of the Ripiphoridae remains uncertain. The two
families were not proposed to be sister group in the earlier molecular
phylogenetic study (Gunter et al. , 2014; Kergoat et al. ,
2014a), which due to the monophyletic status of Ripiphoridae remains
uncertain.
Aderidae was proposed to be a monophyletic lineage in the earlier
molecular phylogenetic study (Gunter et al. , 2014). There is only
species in Aderidae to be included in the present study, which be formed
a monophyly with “Meloidae clade” + “Tenebrionidae clade”, and its
position and monophyletic status are yet to be resolved with more
species to involved. The
“Meloidae clade” + “Tenebrionidae clade”, “Meloidae clade” and
“Tenebrionidae clade” are all proposed to be monophyletic, which are
consistent with earlier studies based on five nuclear and mitochondrial
genes with 300 genera in Tenebrionoidea using ML (Gunter et al. ,
2014) and eight mitochondrial and nuclear gene with 404 taxa in
Coleoptera using ML (Kergoat et al. , 2014a).
Phylogenetic
relationships of “Meloidae clade”
The Meloidae + Anthicidae, Meloidae and Anthicidae are all proposed to
be monophyletic, and the two families demonstrate to be sister groups
each other in the present study. These results are consistent with
earlier studies. The monophyly of Meloidae + Anthicidae was proposed
based on 245 mitochondrial sequences in Coleoptera, including 159 newly
sequenced full or partial mtgenomes using PhyloBayes (Timmermanset al. , 2015). The monophyly of Meloidae was proposed based on 4
818 nuclear genes in 146 species in beetles using ML (Mckenna et
al. , 2019). The monophyly of Anthicidae was proposed based on18S rRNA, 16S rRNA and COX1 gene sequences from
340-taxa using BI (Hunt et al ., 2007), and also based on other
molecular phylogenetic studies (Kergoat et al. , 2014a; Timmermanset al. , 2015; Mckenna et al. , 2019). The sister
relationship of Anthicidae and Meloidae was proposed based on the
morphology characteristics of mesothoracic glands (Hemp and Dettner,
1997), and also based on mitochondrial and nuclear genes (Timmermanset al. , 2015; Mckenna et al. , 2019).
In the “Oedemeridae clade”, the family Prostomidae seems to be located
at the base of “Oedemeridae clade”, followed Oedemeridae and
Trictenotomidae + Tetratomidae. Prostomidae was proposed a sister to the
“pythid-pyrochroid-lineage” (including Trictenomatidae, Pyrochroidae,
Salpingidae and so on) based on morphology characteristics of the
maxillary articulatory area, the abdominal tergite IX extending to the
ventral side of the segment, and the strongly pronounced prognathous
condition (Schunger et al. , 2003). However, Prostomidae and
Tetratomidae are clustered as one clade in ML tree, and the phylogenetic
position of Prostomidae remained unresolved in the present analyses.
The family Oedemeridae is proposed to be monophyletic, which is
consistent with the earlier phylogenetic study based on four gene
(16S rRNA, COX1, 28S and 18S rRNA) sequences from
8441 taxa of Coleoptera, which removed misplaced single specimens and
minor clades (Bocak et al. , 2014). However, it was proposed to be
paraphyletic in the phylogenetic study based on mitochondrial and
nuclear genes (Gunter et al. , 2014; Zhang et al. , 2018),
which suggests that the monophyletic status of the Oedemeridae need be
further determined with more species included. Trictenotomidae and
Tetratomidae are clustered as one
clade using BI in this study, whereas Trictenotomidae was a sister to
Boridae in earlier phylogenetic studies based on nuclear genes (Mckennaet al. , 2019). There is only species in Trictenotomidae and
Tetratomidae to be included in the present study, which suggests that
the monophyletic status of the Trictenotomidae and Tetratomidae remains
uncertain, and its position and monophyletic status are yet to be
resolved with more species to involved.
Zopheridae and Pyrochroidae are
clustered as one clade, and Pyrochroidae seems monophyletic in the
present study. The monophyly of Pyrochroidae was also proposed in the
earlier phylogenetic study based on 95 nuclear protein-coding genes in
373 beetle species using ML and BI (Zhang et al. , 2018), and in
other phylogenetic studies based on mitochondrial and nuclear genes
(Gunter et al. , 2014; Kergoat et al. , 2014a; Mckennaet al. , 2019). Zopheridae was a sister to Tetratomidae in earlier
phylogenetic studies based on mitochondrial and nuclear genes (Kergoatet al. , 2014a), which suggests that the position and monophyletic
status of Zopheridae and Pyrochroidae need be further determined. The
families Salpingidae and Scraptiidae seem monophyletic, and are sister
groups each other in the present study. The monophyly of Salpingidae and
Scraptiidae was also proposed in the earlier phylogenetic studies based
on mitochondrial and nuclear genes (Bocak et al. , 2014; Zhanget al. , 2018; Mckenna et al. , 2019), whereas Scraptiidae
was proposed a paraphyletic group in other molecular phylogenetic
studies (Hunt et al ., 2007; Kergoat et al. , 2014a; Mckennaet al. , 2015). The sister relationship of Salpingidae and
Scraptiidae remains unclear due to the limited inclusion of only two or
three species. Therefore, the position and monophyletic status of
Salpingidae and Scraptiidae need be further determined with more species
included.