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Обзор ископаемых муравьев рода Myrmica ( подсемейство Myrmicinae) из Балтийского и Саксонского янтаря из Позднего Эоцена с описанием новых видов: Myrmica paradoxa n. sp. (Германия) и Myrmica eocenica n. sp. (Россия, Калининградская обл.)
Даны новые комбинации видов: Myrmica rudis (Mayr, 1868b) new combination и Myrmica intermedia (Wheeler, 1915) new combination.
ВВЕДЕНИЕ
Проводя ревизию муравьев рода Myrmica Latreille, 1804, авторы обнаружили в коллекциях Российской Академии Наук и Польской Академии Наук кусочки Балтийского янтаря (Поздний Эоцен, около 40 млн.лет; возможно до Олигоцена, Wheeler, 1915; Larsson, 1978; Bolton, 1995; Dlussky, 1997), каждый из которых включал ископаемые остатки экземпляров Myrmica. Также удачно были исследованы кусочки Саксонского янтаря (того же примерно возраста, что и Балтийский янтарь) из коллекции Manfred Kutscher, которые содержали 3 экз. мирмик. Четыре экземпляра принадлежат двум новым видам: Myrmica paradoxa n. sp. и Myrmica eocenica n. sp. Приводятся их описания и сравнения с другими мирмиками, дается определитель 5 вымерших видов настоящих представителей рода Myrmica.
До сих пор было описано 17 вымерших видов в роде Myrmica (Heer, 1850, 1867; Mayr, 1868b; Novak, 1878; Meunier, 1915): 4 вида из Позднего Эоцена и Олигоцена (около 40–35 млн.лет) и 13 видов из Миоцена (около 25 млн.лет). Однако, только один из них - M. longispinosa Mayr, 1868b - найден в Балтийском янтаре и бесспорно принадлежит к этому роду. Все остальные ископаемые якобы "Myrmica" виды принадлежат к другим родам муравьев. The high number of misidentifications is not surprising because most species were described a long time ago from impressions in rock. Such fossils are very difficult to interpret and identify correctly, even with considerable experience and a good knowledge of recent ant taxonomy.
Три вида "мирмик", M. pusilla Heer, 1850, M. duisburgi Mayr, 1868b и M. rugiceps Heer, 1850 были формально перемещены в другие рода следующими авторами: Handlirsch (1907), Wheeler (1915) и Assmann (1970) соответственно (Mayr, 1867) ... ...
Американский мирмеколог Wheeler (1915) также описал род Nothomyrmica emphasizing
its similarity to Myrmica, from which it differs by only
a single feature (considered very important at that time)—the lack
of spurs on the middle and hind tibiae of workers. It contained
only the four species placed there by Wheeler: N. intermedia
Wheeler, N. rudis (Mayr, 1868b), N. petiolata (Mayr, 1868b) and
N. rugosostriata (Mayr, 1868b); the latter three were first described
in the genus Macromischa Roger, 1863 (now a synonym
of Temnothorax Mayr, 1861; see Bolton, 1995, 2003).
Since many extant Myrmica species are known to have reduced
tibial spurs, or even completely lack them, the feature of reduced
tibial spurs is considered much less diagnostic nowadays (Bolton,
1988a; Radchenko and Elmes, 2003). In our opinion, genus Nothomyrmica
is quite heterogenic and artificially joins unrelated species
(including some Myrmica) having one common feature—the
absence of spurs on the hind and middle tibia. Nothomyrmica
intermedia and N. rudis are very similar to M. longispinosa and
all three closely resemble living species from the M. ritae-group
(Radchenko, 1994; Radchenko and Elmes, 2001b). Therefore, we
formally transfer N. intermedia and N. rudis to the genus Myrmica;
N. rugosostriata is transferred to the newly described extinct
genus Eocenomyrma Dlussky and Radchenko, 2006, and N.
petiolata is transferred to the genus Temnothorax Mayr (Dlussky
and Radchenko, 2006).
Myrmica Latreille, 1804
Myrmica Latreille, 1804, p. 179; type species—Formica rubra Linnaeus,
1758, p. 580, by subsequent designation of Latreille, 1810, p. 437.
Nothomyrmica WHEELER, 1915, p. 60; type species — Macromischa rudis
Mayr, 1868b, p. 85, fig. 85, by original designation; RADCHENKO, 1994, p.
48; BOLTON, 1995, p. 292, n. syn.
Notes. For the diagnosis and full synonymy of the genus Myrmica
see Bolton (1988a, 1995, 2003), Radchenko and Elmes
(2003). Here, we have transferred two of the four Nothomyrmica
species to the genus Myrmica, including type species of Nothomyrmica.
Myrmica paradoxa sp. n.
Diagnosis. Propodeum with two denticles that are short,
straight, wide, blunt at the apex, directed upward and slightly
backward. Frontal carinae short, very weakly curved to merge
with the rugae, which surround antennal sockets. Only anterior
(lower) part of frons with longitudinal rugae, remaining part of
head dorsum with dense but not coarse reticulation. Whole alitrunk
and waist with reticulation. Hind tibiae with conspicuous
pectinate spur.
Description. Head longer than broad, with convex sides and occipital
margin, and broadly rounded, barely marked occipital corners. Eyes of moderate
size, not prominent laterally, situated approximately at the midlength of
lateral margins of head. Anterior clypeal margin very broadly rounded, not
prominent, shallowly notched medially, with pair of long median setae and
fringe of shorter setae on the anterior margin (similar to that of other Myrmica
species). Antennae twelve-segmented and with distinct three-segmented club,
second to ninth funicular joints distinctly longer than broad. Antennal scape
relatively long, at least reaching or slightly surpassing the occipital margin of
head, gradually curved at the base, without any trace of lobe or carina.
Alitrunk short, wide, and robust. Promesonotum feebly convex (in lateral
view) and in dorsal view with broadly rounded anterio-lateral corners, distinctly
narrowing posteriorly (approximately twice wider anteriorly than posteriorly),
without any trace of a promesonotal suture. Metanotal groove distinct,
abrupt but not very deep. Dorsal surface of propodeum subequal to its
declivity (= posterior surface), propodeal lobes not sharply pointed, at most
bluntly angulated at the apex. Petiole with relatively short but distinct peduncle,
its node quite massive, with rounded dorsum. Postpetiole subglobular and
lower than petiole (in lateral view).
Body with rather abundant, suberect to erect, moderately long, thin, pointed
hairs. Antennal scape with subdecumbent to suberect hairs; hind tibiae and
femora with short subdecumbent hairs, but with longer suberect hairs on the
inner margin of femora.
Etymology. The species named for its paradoxical combination of features.
Material examined. Three workers (holotype and paratypes in the same
piece of amber), GPMHU, No F-199, Germany, Saxonian Amber.
Measurements (mm) and indices. Holotype: HW 1.12, FW 0.42, FLW
0.50, SL 0.99, AL 1.57, PNW 0.95; FI 0.38, FLI 1.20, SI2 0.89. Paratype
specimen one: HL 1.27, SL 0.92, HTL 0.87; SI1 0.73. Paratype specimen two:
PL 0.46. Body length is ca. 6 mm.
Discussion. Myrmica paradoxa n. sp. well differs from any
other known modern or fossil Myrmica species, especially by the
very short propodeal denticles: such a shape of propodeal armature
is peculiar, unknown in any modern or other fossil Myrmica
species. It is paradoxical because on one hand it is characterized
by features that are quite normal for the genus Myrmica, but on
the other hand, others that are not known from any other Myrmica
species. Thus, while it has a sculpture and shape of the head,
pilosity of the body, shape of petiole and postpetiole and a distinct
pectinate spurs on the hind tibiae that are typically Myrmica, its
very well marked three-jointed antennal club and the generally
short and robust alitrunk with the short blunt propodeal denticles
are atypical. No other extant Myrmica species has such a short
dorsal surface of the propodeum relative to the posterior surface
(the propodeal declivity) and only the unusual queens of Myrmica
luteola Kupyanskaya, 1990 have short propodeal denticles. Unfortunately,
the maxillary and labial palpes, which can be diagnostic
of certain genera, are invisible. We consider that most probably,
M. paradoxa represents an extinct lineage within the genus.
Myrmica eocenica sp. n.
Diagnosis. Propodeum with very long, straight propodeal
spines, that are directed backwards, strongly divergent (in dorsal
view). Frontal carinae very weakly curved, not curving outwards,
merging with the rugae, which run backwards to the occipital
margin of the head. Body with coarse sculpture. Hind tibiae with
conspicuous pectinate spur.
Description. Head distinctly longer than broad, with convex sides,
straight occipital margin, and narrowly rounded occipital corners. Eyes relatively
small, convex, situated approximately at the midlength of lateral margins
of head. Anterior clypeal margin narrowly convex, but not prominent,
without notch, with pair of long median setae and fringe of shorter setae on
the anterior margin (similar to that of other Myrmica species). Frons wide;
frontal lobes slightly extended, quite narrow and pointed at the apex. Antennae
twelve-segmented and with three (possibly four?)-segmented club, funicular
joints second to eighth distinctly longer than broad. Antennal scape long,
surpassing occipital margin of head, very feebly curved at the base, without
any trace of lobe or carina. Frons between frontal carinae with only three
coarse longitudinal, slightly sinuous rugae, which reach occipital margin; its
lower (anterior) part between frontal lobes with four additional short longitudinal
rugae, which extend only to the level of the eyes; upper (rear) part of
frons and remainder part of head dorsum with coarse reticulation. Antennal
sockets deep and surround by at least one coarse ruga. Clypeus with coarse
longitudinal rugosity.
Alitrunk relatively long and slender. Promesonotum somewhat flattened (in
lateral view), with narrowly rounded anterio-lateral corners and with trace of
promesonotal suture (in dorsal view). Metanotal groove distinct, but not very
deep. Dorsal surface of propodeum somewhat longer than posterior one, propodeal
lobes sharply pointed at the apex. Petiole with long peduncle, its node
low and long, with weakly convex dorsum, postpetiole fig-shaped (in dorsal
view). Whole alitrunk with coarse reticulation, only propodeal dorsum seems
to be also having short longitudinal rugae (the last feature is not clearly visible
in the investigated specimen). Petiolar node with longitudinally-concentric
rugae, its dorsum also with moderate (not coarse) reticulation, postpetiole in
dorsal view with longitudinal rugae.
Body with a few, suberect to erect, thin, pointed hairs. Antennal scape,
hind tibiae and femora with sparse subdecumbent, quite long hairs; inner
margin of femora has longer suberect hairs.
Etymology. The species named after geological epoch when the type
specimen was trapped in amber.
Material examined. One worker, holotype, PIN, 964/479, Kaliningrad
Province of Russia, Baltic Amber.
Measurements (mm) and indices. HL 1.11, HW 0.95, FW 0.41, FLW
0.52, SL 1.06, AL 1.34, ESL 0.63, ESD 0.62, HTL 0.91; CI 1.16, FI 0.43,
FLI 1.28, SI1 0.96, SI2 1.12, ESLI 0.66, ESDI 0.98. Body length ca. 6.5 mm.
Discussion. Myrmica eocenica n. sp. is similar to all the previously
described Myrmica species from Baltic Amber. Unfortunately,
types of all others appear to be lost (see above), so this
comparison is based solely on Mayr’s and Wheeler’s original descriptions
and drawings.
It differs from M. longispinosa by its sharply pointed apically
propodeal lobes, by the strongly divergent propodeal spines (compare
Figs. 1.1 and 4, 5), and by its somewhat longer body ( 6
mm vs. ca. 5 mm). Compared to the former ‘‘Nothomyrmica’’
species, it differs by its well developed pectinate spurs on the
hind tibiae; though this feature may be not so distinctive at the
generic level (see above), it is usually more constant at the species
level. It clearly differs from M. rudis by the shape of the propodeal
spines and petiole: in M. rudis the spines are somewhat
curved and directed backward and upward while its petiole has a
much shorter peduncle and subtriangular node (compare Figs. 1.2
and 4, 5). Myrmica eocenica most resembles M. intermedia by
the shape and sculpture of its body but, apart from the tibial spurs,
it also differs by its straight and strongly divergent propodeal
spines (compare Figs. 1.3 and 4, 5), and body length ( 6 mm
vs. 4.7 mm). Generally, M. eocenica is very similar to living
species of the ritae-group of Myrmica (see Radchenko, 1994;
Radchenko and Elmes, 1998, 2001b) and almost certainly should
be placed in this group.
Myrmica longispinosa Mayr, 1868b new comb.
Occurrence. Kaliningrad Province of Russia, Baltic Amber.
Myrmica rudis (Mayr, 1868b) new comb.
=Macromischa rudis MAYR, 1868b,
=Nothomyrmica rudis (Mayr, 1868b).
Occurrence. Kaliningrad Province of Russia and northwestern Poland,
Baltic Amber.
Myrmica intermedia (Wheeler, 1915) new comb.
=Nothomyrmica intermedia WHEELER, 1915
Occurrence. Kaliningrad Province of Russia, Baltic Amber.
ДИСКУССИЯ
Большинство учёных рассматривают трибу Myrmicini (включающую роды Myrmica,
Manica Jurine, 1807, Eutetramorium Emery, 1899, Hylomyrma
Forel, 1912, Pogonomyrmex Mayr, 1868a и Secostruma
Bolton, 1988b) в качестве наиболее морфологически базальной в подсемействе
Myrmicinae, based on the plesiomorphic state of features,
such as the structure of the mesosoma with well defined sutures,
six-jointed maxillary and four-jointed labial palpes, and the presence
of pectinate spurs on the mid and hind tibia. A recent molecular
phylogeny of ants (Moreau et al., 2006) suggests that subfamily
Myrmicinae arose more than 100 Ma prior to a huge
diversification of ants that the authors believe was related to the
evolution of angiosperm plants. By the Late Cretaceous (about 80
Ma) the subfamily already comprised five or so, distinct (‘‘old’’)
lineages and most of the modern genera were established during
the next 35 million years before the start of the Eocene. Interestingly,
they found that the three studied representatives from tribe
Myrmicini fall in two of the ‘‘old’’ lineages: Myrmica and Eutetramorium
are in one, while Pogonomyrmex is in another that
includes Messor Forel, 1890 and Aphaenogaster (both latter genera
belong to the tribe Pheidolini). When an even more detailed
molecular phylogeny is made, the tribe Myrmicini will probably
have to be revised.
Мирмекологи Radchenko and Elmes (2001b) считают, что анцестральные
Myrmicini вероятно были наиболее сходны с современными Myrmica, или возможно
Manica, because the other four genera possess many derived
features (see Bolton, 2003 and literature cited therein). They
had considered that any resemblance between Messor and Pogonomyrmex
was solely due to convergent evolution, but the Moreau
et al. study (loc. cit.) suggests otherwise. Despite Manica
species appearing to have more plesiomorphic features, e.g., a full
complement of mesosomal sutures with some large specimens
having a rudimentary scutellum, filiform antennal funiculus in
males, Radchenko and Elmes (2001b) believed Manica and Myrmica
most probably derived from a common ancestor at about
the same time. Unfortunately Moreau et al. (2006) did not sample
Manica species, but the general thrust of their results support that
idea. Furthermore, if both genera arose 60–70 Ma during a burst
of ant diversification and before North America was completely
separated from Eurasia, it would explain both the modern distribution
of Manica (restricted to North America except for two
species) and the general dissimilarity between North American
and Eurasian Myrmica species-groups.
Четыре из пяти известных ископаемых видов рода Myrmica очень сходны с современны ми представителями группы
ritae-group. These species are usually considered
as basal in relation to the extant forms (Radchenko, 1994;
Radchenko and Elmes, 2001b; and above). They are very poorly
represented in collections and were considered to be unusual and
rare until recent studies showed that they are relatively numerous
and common in certain subtropical forests on mountains in the
extreme southeastern part of the Palaearctic and in the north of
the Oriental Regions (Radchenko and Elmes, 1998, 1999, 2001a,
2001b; Radchenko et al., 2001). Some species are superficially
very similar to Aphaenogaster (tribe Pheidolini) and are frequently
misidentified as such (see Radchenko and Elmes, 1998) but we
believe that this is genuine convergence similar to, for example,
that between Cataglyphis FoЁrster, 1850 (tribe Formicini) and Myrmecocystus
Wesmael, 1838 (tribe Lasiini). Weber (1950) also noted
that M. ritae Emery, 1889 and related species have similar
characteristics to some tropical species of Aphaenogaster and
therefore suggested that they might have similar habits, such as
a more arboreal way of life than is normal for Myrmica. Indeed,
recent field studies of some ritae-group species (G. W. Elmes, A.
Schulz, and K. Eguchi, personal commun., 2003) suggest that
some species might live and forage entirely on trees.
We suggest that the putative ancestor of modern Myrmica lived
in the warm early Eocene forests and by the late Eocene had given
rise to M. ritae-like species and other unusual forms, such as the
extinct M. paradoxa n. sp. or extant M. mirabilis Elmes and Radchenko,
1998. While it is possible that the ancestors of most other
modern Myrmica species-groups had by this time already developed
a greater cold tolerance and had penetrated the more northerly
temperate forest zone, it is unlikely because there is a total
absence of Myrmica specimens in the Oligocene and Miocene
deposits of Eurasia that are associated with temperate conditions,
despite the presence of quite a rich ant fauna, including several
Aphaenogaster species that are morphologically and ecologically
similar to Myrmica (Theґobald, 1937; Dlussky, 1981; Zhang,
1989). More probably, ancestor(s) of the different modern species-
groups remained restricted to the warmer Eocene forests, coexisting
with M. ritae-like species. Given our current understanding
of the available fossil records and the paucity of fossil
Myrmica, represented by only a few specimens found in amber
deposits, we suggest that at the end of the Eocene, Myrmica species
might have been generally rare with restricted distributions.
Yet, some of the early Myrmica species survived the ecological
trauma of the post-Eocene cooling and adapted to the cooler habitats.
Unfortunately, there are no data on the Pliocene ant fauna of
Eurasia to indicate how adaptive radiation proceeded to the extent
that Myrmica is now one of the dominant ant genera of the temperate
Holarctic, whether measured in terms of the number of
species, colonies or individuals. Indubitably, isolation due to alternating
glacial ages of the last millions of years played an important
role in subsequent speciation. On the other hand, typical
ritae-group species and a few other basal forms, for example M.
mirabilis (rather similar to Manica in the general shape of the
body, but in other features clearly Myrmica), were confined to
forests on high mountains in subtropical South and Southeast
Asia, where many species of plant and animal found in late Eocene
amber still persist (Larsson, 1978).
Интересно, что большинство современных видов Myrmica с предположительно
базальными морфологическими чертами в основном обнаружены в южных горных системах.
There are numerous unusual and endemic Myrmica
species, including presumably basal forms, in the southwestern
Himalayas, which were isolated from the rest of the Myrmica
fauna at some time in the late Miocene – early Pliocene.
We have found some similar atypical Myrmica in the mountains
of Turkey (Elmes et al., 2002) and few unusual species have been
described from the southern mountains of the USA (see also Radchenko
and Elmes 2001b). Almost certainly, more rare, basal
forms of Myrmica remain to be discovered in the southern mountains
of North America. It would not surprise us if species similar
to M. ritae were discovered on high mountains in Mexico, since
Tertiary flora and fauna have persisted in the Americas because
migration in response to climate change is facilitated by the northsouth
orientation of mountain systems.
Морфология ископаемы Myrmica, discussed above, suggest
that female castes of the ancestral species probably had long,
gently curved antennal scape, with no thickening or lobes. A short
scape in males is plesiomorphic evolutionary condition for all ants
(Dlussky, 1983; Dlussky and Fedoseeva, 1988); therefore the
males of the ancestral Myrmica species probably had short antennal
scapes. This is the case in most ritae-group species for which
this character is known (Radchenko and Elmes, 1998). The two
morphological features that are most important in defining modern
species-groups (sharply angled antennal scape of the female
castes and longer antennal scape among males, see Radchenko
and Elmes, 2001b) probably derived from the ancestral form during
the adaptive radiation of Myrmica following the post-Eocene
cooling.
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