Siren intermedia Barnes, 1826

Fedler, Matthew T., Enge, Kevin M. & Moler, Paul E., 2023, Unraveling Siren (Caudata: Sirenidae) systematics and description of a small seepage specialist, Zootaxa 5258 (4), pp. 351-378 : 369-374

Siren intermedia Barnes, 1826

( Figs. 1‒7 , 9 , 10 , & 13)

Common name. Intermediate Siren

Neotype: UF Herp 190369 ( Fig. 7A ), adult female (gravid) from Wayne Co., Georgia, USA (31.50109°N, 81.91324°W, datum WGS84, elev. 13 m). Collected on 30 January 2020 by Dirk Stevenson, Arik Hartmann, and Matthew Fedler.

Description of neotype: The neotype has 32 costal grooves and faint black spots on the dorsum extending from the head to the fourth costal groove behind the forelimbs. In life, it had a bluish gray venter and sides and a dark grayish brown dorsum. The slightly darker tail tip may indicate old regeneration. A broken chartreuse labial stripe runs from a few millimeters posterior of the nares to just anterior of the gills. Light yellow spots are present ventrolaterally on the head, often surrounding sensory pores. Sparse and more randomly placed small (<3 mm) yellow spots are posterior to the gills on the forelimbs and lateral/ventrolateral portions of the body, terminating roughly one-third of the distance between forelimbs and cloaca. The gills have sparse, minute, chartreuse yellow spots. Minor abrasions are present near the cloaca. Measurements are 146 mm SVL, 85 mm TaL, 6.3 mm interorbital distance, 12.9 mm head width, 18.5 mm head length, 5.8 mm eye-snout distance, and 8.4 mm chest width.

Paratypes: UF Herp 188598, 189657 ( Fig. 7B ), 188604 ( Fig. 7C ), 188605 ( Fig. 7D ), 186989 ( Fig. 7F ), 190370 ( Fig. 7E ), 190371, 190374, 190375. Locality information for these specimens can be found via the Florida Museum of Natural History’s web database (http://specifyportal.flmnh.ufl.edu/herps/) .

Diagnosis. Siren intermedia has typical Siren characteristics: external gills with three fimbriate gill stalks, three associated gill slits, four toes on the forelimbs, lack of pelvic girdle and hindlimbs, and a thin, pigment-bearing mucus layer that overlies the keratinized skin. This species is best distinguished from other sympatric Siren lineages by costal groove count, which varies geographically. We restrict this species to the recovered S. intermedia lineages A, B and C. All S. intermedia lineages combined that we examined have 29‒33 costal grooves ( Fig. 4 ). Lineage B has a more restricted costal groove range of 29 (n =12), 30 (n = 23), or 31 (n = 3) in areas of sympatry with S. sphagnicola ., which has 31‒33 costal grooves in the East Bay, Yellow, Blackwater, and Escambia river drainages. Specimens of lineage B that are comparable in size to S. sphagnicola typically have yellow labial stripes, rostral patches, and ventrolateral flecking ( Fig. 10 ).

Siren intermedia lineages A (type clade) ( Fig. 7 ) and C ( Fig. 10 ) can be distinguished from sympatric Siren species by having fewer than 34 costal grooves. These two lineages exhibit hypervariability in pattern and coloration. Yellowish labial stripes and rostral patches may be present or absent. Numerous distinct black spots may be present, absent, or occur in patches on the dorsal and lateral surfaces of the head and body, and some individuals possess reticulated patterns (UF Herp 186989, 192033, and an unvouchered specimen from the same locality as 192033). These traits are also present in other Siren species and may be variable within populations of any of these species, emphasizing the need for accurate costal groove counts to distinguish from other species in the vicinity.

Original description, first redescription, and comments. Le Conte (1828) provided the following description: “Its greatest length is twelve inches: colour uniform dusky, very slightly paler beneath, sometimes faintly speckled with darker above.” Barnes (1826) and Harlan (1827) announced that the species was going to be described and provided the same information when summarizing Le Conte’s forthcoming manuscript.According to Harlan (1827): “Colour resembling that of the Lacertina; branchiae resembling those of the Striata [i.e., Pseudobranchus striatus Le Conte ]. Length about one foot.”

We designated a neotype from near the type locality for the express purpose of clarifying the taxonomic status of a nominal taxon whose specimens (syntypes) were destroyed. Smith et al. (1975) clarified that the name should be attributed to Barnes (1826). Le Conte’s (1828) description provided additional traits that are generic among Siren and failed to identify any features that distinguish it from other Siren given our current understanding of the genus. Siren intermedia is extremely variable in both color and pattern, and many phenotypes overlap those of S. lacertina and S. nettingi .

The original type locality was purportedly Le Conte’s Woodmanston Plantation, Riceboro, Georgia ( Harper 1935). We chose the neotype locality, which is approximately 45 km SW of Woodmanston Plantation, because all sequenced specimens from the surrounding region and Altamaha River drainage belong to the same mtDNA lineage as our single Woodmanston Plantation specimen. The neotype locality is easily accessible and yielded many S. intermedia compared to other localities in the area. Additionally, the locality has stereotypical habitat for S. intermedia consisting of a cypress swamp with many small creeks and large accumulations of muck, leaf packs, and submerged Creeping Rush ( Juncus repens [Michaux]).

Noble and Marshall (1932) provided a redescription of S. intermedia but failed to state where the specimens they examined came from, and they likely included specimens from populations later split into the nettingi and texana subspecies of S. intermedia . This would explain their higher costal groove range for S. intermedia (up to 36 grooves). Additionally, they stated that the outer capsule of the egg was wider for S. lacertina than S. intermedia . This may ultimately be proven true by future studies, but their data are contradictory in light of the revised Siren taxonomy. Noble and Marshall (1932) compared specimens of what they considered to be S. intermedia and S. lacertina from the same locality (Maverick Co., Texas) to each other, as well as S. intermedia and S. lacertina from Oakley, Berkeley Co., South Carolina. A recent genetic study ( LaFortune 2015) found that the Rio Grande drainage has only one genetic group of Siren ; thus, Noble and Marshall (1932) and Flores-Villela and Brandon (1992) were comparing large and smaller individuals of the same species (now S. nettingi ) using different names. Their findings indicate that different-sized individuals of the same species may have different-sized eggs, or they were comparing specimens with eggs at various stages of development.

Size. The largest specimen we examined (UF Herp 186989) measured 191 mm SVL and 125 mm TaL (316 mm TL). Noble & Marshall (1932) reported a male S. intermedia (MCZ Herp A-140) from Georgetown, South Carolina, that measured 212 mm SVL and 347 mm TL. This animal is likely a member of S. intermedia lineage C. Goin (1957) provided 240 mm SVL and 381 mm TL for the maximum size of “ S. i. intermedia ” specimens he examined. However, he failed to provide the collecting locality or attribute the measurements to a vouchered specimen; thus, we are unable to assign it to a lineage. Because Goin assumed that only S. i. intermedia was present in the coastal drainages of Mississippi, Alabama, and the Florida Parishes of Louisiana, he may have attributed the size to a specimen that we now recognize as S. nettingi . Furthermore, his measurements closely match the size of the largest S. nettingi specimen we sequenced (LSUMZ 87289; 270 mm SVL, 408 mm TL) and the largest S. nettingi in the AUM collection (AUM 40435; 242 mm SVL, 365 mm TL). The smallest sexually mature female (UF Herp 190904) measured 75 mm SVL and 119 mm TL.

Distribution. Our findings restrict S. intermedia to Atlantic and Gulf drainages from the vicinity of Chesapeake Bay south to central Florida and west throughout the Florida panhandle ( Fig. 9 ). Specimens attributed to this species from the Mobile Bay drainage westward are likely either S. nettingi or S. sphagnicola .

Common name. The first common name assigned to S. intermedia was Intermediate Siren ( Gray 1831) , and we suggest using this name instead of Lesser Siren because there are three larger sirens ( S. lacertina , S. reticulata , S. nettingi ) and three smaller sirens ( S. sphagnicola , Pseudobranchus axanthus , P. striatus ). This also aligns the epithet with the common name.

Specimens examined. See Supplemental Table 1 .

Figures

FIGURE 1. Bayesian probability tree of concatenated 16S and ND4 regions inferred using BEAST2. Individual specimen labels include voucher ID or GenBank number if no voucher, state, county, and lineage.

FIGURE 2. Median joining networks of Siren haplotypes for RAG1 (left) and NCX1 (right) regions made using PopART.

FIGURE 3. Box plots with points colored by sex showing distribution of tail proportions of Siren lineages. Outliers are noted with red triangles on the associated box plot.

FIGURE 4. Box plots with points representing specimens per showing distribution of costal groove counts of Siren lineages.

FIGURE 5. Box plots of the distributions of snout-vent length and the five size-corrected linear measurements compared using linear discriminant analysis.

FIGURE 6. Results from our linear discriminant function analysis based on the five size-corrected linear measurements taken from 396 Siren specimens. Except for S. reticulata, each lineage failed to create meaningful separation.

FIGURE 7. Live Siren intermedia type specimens belonging to mtDNA lineage A. A Neotype from Wayne Co., Georgia (UF Herp 190369). B Paratype from McIntosh Co., Georgia (UF Herp 189657). C Paratype from Nassau Co., Florida (UF Herp 188604). D Paratype from Nassau Co., Florida (UF Herp 188605). E Paratype from Wayne Co., Georgia (UF Herp 190370). F Paratype from Lake Co., Florida (UF Herp 186989).

FIGURE 9. Distribution map of specimens assigned to Siren intermedia (orange circles) and S. nettingi (blue circles). The red line is the eastern boundary of the Mobile drainage from EDNA Derived Watersheds for Major Named Rivers (https://edna. usgs.gov/watersheds/kml_index.htm). The Mobile drainage lacks S. intermedia records and is the easternmost drainage where S. nettingi occurs. Our westernmost records of S. intermedia are from the Escambia drainage.

FIGURE 10. Live Siren intermedia specimens belonging to mtDNA lineages B and C. A Lineage C from Berkeley Co., South Carolina (UF Herp 188612). B Lineage C from Berkeley Co., South Carolina (UF Herp 188613). C Lineage B from Holmes Co., Florida (UF Herp 188769). D Lineage B from Jackson Co., Florida (UF Herp 188901). E Head of lineage B specimen from Holmes Co., Florida (UF Herp 188769). F Head of lineage C specimen from Berkeley Co., South Carolina (UF Herp 188612) (lineage C). G Head of lineage C specimen from Berkeley Co., South Carolina (UF Herp 188613). The latter two specimens are from the same locality but differ dramatically in pattern and coloration.