Dendrocephalus (Dendrocephalinus) proeliator, 2019

Rogers, D. Christopher, Dunn, Ann & Price, W. Wayne, 2019, A review of Dendrocephalus (Dendrocephalinus) (Crustacea: Anostraca) with the first records of male-male anostracan aggressive competition, European Journal of Taxonomy 509, pp. 1-14 : 6-10

Dendrocephalus (Dendrocephalinus) proeliator sp. nov.

urn:lsid:zoobank.org:act:203C0A81-A3CD-4A02-9001-47259EE2EA7C

Fig. 2

Diagnosis

Males are typical of the subgenus Dendrocephalinus , and readily identified in that the frontal appendage primary arms are each triramal, with branch 2A bearing an apical hamulate projection. The antenna-like appendage is extremely small and may be obscured. Females are not separable.

Etymology

The specific epithet ‘ proeliator ’ is Latin for ‘warrior’. The gender is masculine.

Material examined

Holotype USA • ♂; Florida, Dade County; 25°34.781΄ N, 80°34.541΄ W; 1.5 m a.s.l., on west side of SW 237 th Avenue, south of Grossman Hammock ; 30 Jul. 2001; E.L. Nance leg.; FLMNH Type 49581 .

Allotype

USA • ♀, same data as for holotype; FLMNH Type 49582.

Paratypes

USA • 4 ♀♀, 1 ♂; same data as for holotype; FLMNH Type 9041 .

Other material USA • 28 ♀♀, 26 ♂♂; Florida, Highlands County, Archbold Biological Station, Pond # 107.1; 27°11΄36.24˝ N, 81°21΄29.88˝ W; 41 m a.s.l.; 1 Jul. 2016; A. Dunn; cultured material; DCR-976.

Type locality

The type locality is Pond #107.1 at the Archbold Biological Station; a temporary pool in calcareous wet prairie. The substrate is Duette Sand, the pool fills to a maximum observed depth of 10 cm, and the subcircular basin is approximately 15 m across. These soils are calcareous and have a salinity of ~2 mS/ cm. The basin substrate has 100% vegetative cover, dominated by approximately 70% yellow hatpin ( Syngonanthus flavidus (Michx.) Ruhland, 1903 ) and 30% Florida bluestem ( Andropogon floridanus Scribn., 1896 ). A cluster of scrub oaks (possibly Quercus geminata Small, 1897 ) is in the center, providing shade and leaf litter. The surrounding area is scrubby flatwoods; a mixture of saw palmetto and shrubs with scattered pitch pine.

Description

Male LENGTH. Average length of preserved material: 4.5 mm (males) and 8.2 mm (females) from apex of head to apex of telson.

HEAD ( Fig. 2A ). Male anteriolateral corner of head slightly projecting over eyestalk base. Labrum smooth. Antenna-like appendage anteriobasal to eyestalk, filiform, obscure, length approximately 0.1× eyestalk peduncle. First antenna approximately 85% the length of eye plus eyestalk. Second antenna capable of extending to thoracomere II or III. Second antennal proximal antennomere subcylindrical, smooth, with length approximately 3.0× distoapical width. Proximal antennomere distal end with short, medial, lobiform projection. Projection protruding slightly distally, smooth, apically rounded, length approximately 0.1× antennomere. Second antennal distal antennomere length slightly longer than proximal antennomere, flattened anterioposteriorly, gently arcuate medially, with apex acute and directed medially. Medial edge distal ~55% margined with fine, aciculate denticles, directed subdistally. Cephalic appendage prominent, typical of the subgenus. Proximal trunk subcylindrical, smooth, lacking spines. Primary branches smooth, lacking spines, diverging approximately even with the distal end of the second antenna proximal antennomere. Primary branch triramal. Distal branches diverging at distal end of primary branch. Primary branch length ~3.4 × proximal trunk. Branch 2V thick, flattened, with numerous semiannulations. Length ~0.7 × primary branch. Apex tapering in distal third. Distal fourth with four lateral lobes on each margin. Lobes and apex tipped with an acute spine. Spine length ~2.5 × basal width. Branch 2D flagelliform, subequal in length to primary branch, lacking spines or setae. Branch 2A roughly triangular, with a chitinised tumid area covering approximately one third of the lateral surface, bearing rows of large chitinised, spiniform projections. Spiniform projections smaller distally and medially, length ranging from ~0.5 × to 1.0 × basal width. Spiniform projections posteriorly and laterally becoming larger, subcylindrical, length ranging from ~1.0 × to 2.0 × basal width, each bearing an apical ring of spinulae. Spinulae number three to five per projection. Branch 2A distally chitinised, hamulate, with apex subacute. Distal hamulate projection chitinised, length ~0.25 total branch 2A length. Maxillae lobiform and transverse, no setae visible.

THORACOPODS ( Fig. 2C ). Serially homologous. Thoracopod V with endites margined with long, plumose setae. Endite VI with two distal spines. Endopod subquadrate, with distal margin bearing a submedial emargination. Endopod with distomedial margin bearing a row of acute spines, length ~3 × basal width, separated by their basal width. Endopod distal margin mesad of emargination with four spines, slightly curved posteriorly, length ~4 × basal width, separated by their basal width. Endopod distal margin lateral of emargination bearing a row of cirriform setae, length ~5.0 × to 6.0 × the distal spines. Endopod of all thoracopods, except thoracopod I lack setae on basomedial margin. Thoracopod I and II endopods as in other limbs, although the basomedial margin bears a few obscure filiform setae. Exopod lamellar, sinuate, margined in distal half with long, plumose, recurved setae. Epipodite elliptic and without marginal setae. Margins crenulate. Praepipodite broadly triangular, lamellar, without marginal setae, bearing a light mediolateral cleft.

GENITALIA. Genital segments smooth. Retracted gonopod as for genus. Everted gonopods not observed. Abdomen smooth, cercopods ¾ as long as abdomen, margined with plumose setae.

Female

Generally as typical for the genus ( Fig. 2B ).

HEAD. Rounded, anterolateral corners slightly projecting over eyestalk base. First antenna length 0.25 × second antenna. Second antenna broadly elliptic, lamellar. Thorax smooth. Thoracopods as in male, except endopods lacking emargination.

BROOD POUCH. Fusiform, extending to proximal margin of postgenital abdominal segment IV.

Eggs Subspherical, diameter approximately 190 μm, with large, broad pentagonal or quadragonal facies, each face diameter approximately 60 μm ( Fig. 2D ).

Differential diagnosis

Of the four species of Dendrocephalus (Dendrocephalinus) , males of D. proeliator sp. nov. are morphologically intermediate between D. lithacus ( Fig. 1C ) and D. alachua ( Fig. 1B ). These three species are easily differentiated from D. acacioidea ( Fig. 1A ) which lacks branch 2A in the frontal appendage. The three remaining species bear the lateral, broad surface of branch 2A with its rows of spiniform projections. Dendrocephalus proeliator sp. nov. bears three rami, as does D. alachua , and the three rami are superficially similar in overall structure between the two taxa. However, the hamulate distal projection of D. proeliator sp. nov. is absent in D. alachua . This hamulate distal projection is present in D. lithacus .

Dendrocephalus proeliator sp. nov. is further separated from D. alachua in that branch 2V has eight total lateral lobes verses nine in D. alachua , and branch 2D is long, flagelliform and smooth in D. proeliator sp. nov. instead of vermiform and bearing rings of spines in D. alachua . Furthermore, branch 2D is proportionately much longer in D. proeliator sp. nov. than in D. alachua . Dendrocephalus alachua also has a distomedial spiniform projection at the apex of the second antennal distal antennomere, which is lacking in D. proeliator sp. nov.

Dendrocephalus lithacus lacks the branch 2D found in the other two species, and branch 2A is proportionately larger and more robust than the condition found in D. proeliator sp. nov. The hamulate projection of branch 2A in D. proeliator sp. nov. is approximately one fourth the total length of the branch, whereas in D. lithacus it is nearly half the branch length. Dendrocephalus lithacus also bears a row of fine spinulae on the second antenna proximal antennomere just basal to the frontal appendage, and a second row on the posteriolateral margin of the frontal appendage main trunk. These are lacking in D. proeliator sp. nov. and D. alachua . The second antennae distal antennomere medial margin bears spaced transverse grooves in D. lithacus versus a row of fine denticles in D. proeliator sp. nov.

Distribution and habitat

So far, this species is only known from two locations in southern peninsular Florida. Both sites are temporary pools in calcareous wet prairie. Both sites are in sandy loam soils, with 50–90% calcium carbonate, and salinity around 2.0 mS/cm.

The pool south of Grossman Hammock is inside Everglades National Park, in an area of state managed lands in Water Conservation Area 3B ( Kambly & Moorehead 2009). The type locality resides within the land managed by the Archbold Biological Station, established in 1941 by Archibold Expeditions, a non-profit, independent research organisation, based in Florida.

Due to the limited distribution of D. proeliator sp. nov., this species meets the IUCN red list CR B1a,b species criteria (IUCN 2000), which means the species is ‘Critically Endangered’, with an extent of occupancy less than 100 km 2, and a projected decline in extent of occurrence. It is our hope that future surveys will find additional populations.

Behaviour

Mate searching behaviour was described in detail by Rogers (2019). Anostracans engage in hill topping behaviour, wherein salient objects are used as congregation points for males and receptive females. We observed this same hill topping behaviour in D. alachua and D. proeliator sp. nov. However, both species engaged in male-male agonistic interactions, wherein males actively attempt to drive each other away from hill topping points.

Males would patrol salient objects as described by Rogers (2019). When another male was encountered ( Fig. 3A ), they would attempt to inspect each other as potential mates (sensu Rogers 2019), but in attempting to inspect, each would not let the other beneath them, and they would circle, always facing each other ( Fig. 3B ). This would lead to instances of butting heads and actively feeling each other with the first antennae ( Fig. 3C ), interspersed with more circling. Occasionally, one would be able to get past its opponent’s head and push them on the side ( Fig. 3D ). Typically, if a male had eyes closer set, or was pushed once or twice on the side, it would flee the other male ( Fig. 3 E–F). Presumably, the male with the wider set eyes would be larger and so the smaller one would flee to find a new hill topping site.

The activity of the first antennae during these encounters may be entirely tactile, or there may be some sort of chemosensory occurring as is observed in agonistic behaviour in crayfish ( Bergman & Moore 2005).

Figures

Fig. 2. Dendrocephalus proeliator sp. nov. Paratypes; Florida, Dade County; FLMNH Type 9041. A. Male head, anterior view. B. Female, right lateral view. C. Right limb V, anterior view. D. Two examples of the egg. Abbreviations: 1V = first ventral branch; 2A = apical branch; 2D = dorsal branch (terminology follows Pereira 1983). Scale bar: A = 2 mm; B = 7 mm; C = 1 mm; D = 1.5 mm.

Fig. 1. Dendrocephalus spec. A. Dendrocephalus acacioidea, male head, left side, anterior view. B. Dendrocephalus alachua, male head, left side, anterior view. C. Dendrocephalus lithacus, male head, left side, anterior view. D. Dendrocephalus acacioidea, brood pouch, right, lateral view. E. Dendrocephalus alachua, brood pouch, right, lateral view. F. Dendrocephalus lithacus, brood pouch, right, lateral view. G. Dendrocephalus lithacus, male, labrum, ventral view. H. Dendrocephalus lithacus, gonopods, right, lateral view. Scale bar: A–C = 1 mm; D–F, H = 4 mm; G = 0.25 mm.

Fig. 3. Dendrocephalus proeliator sp. nov, male-male aggressive interactions. A. Encounter. B. Circling. C. Head to head attack. D. Broadside attack. E–F. Chasing.