SIZE-FECUNDITY RELATIONSHIPS AND THEIR EVOLUTIONARY IMPLICATIONS IN FIVE DESMOGNATHINE SALAMANDERS STEPHEN G. TILLEY Museum of Zoology, University of Michigan, Ann Arbor Received June 5, 1968 The plethodontid salamander genus Des­ genus has been "the gradual transformation mognathus comprises seven species accord­ of a population with a high egg production ing t.o current taxonomy, of which six and low survival into a population with low occur in, and four are endemic to the Ap­ egg production and a high survival to ma­ palachian Mountain system of eastern turity." He found no differences in num­ North America. Over most of the southern ber of clutches per year or age at maturity Blue Ridge Physiographic Province several that might compensate for differences in of these forms may exist sympatrically. An clutch size. apparent maximum of sympatry occurs in This paper attempts to further explore the Balsam Mountains of southwestern Vir­ and compare the relationships between size ginia, where five species, D. quadramacu­ and fecundity among the five sympatric latus, D. monticola, D. fuscus, D. ochro­ species of Desmognathus and to elaborate phaeus, and D. wrighti occur in abundance. on the hypotheses drawn by Organ relative Organ (1961) studied the ecological rela­ to evolutionary trends in reproductive tionships and population dynamics of these habits. In particular I have sought to species at Whitetop Mountain and Mt. determine whether fecundity differences Rogers in the Balsam Mountains. Hairston among the five species are explained simply (1949) compared the ecologies of D. by differences in their sizes, or whether size­ quadramaculatus, D. monticola, D. ochro­ fecundity relationships are more complex. phaeus, and D. wrighti in the Black Moun­ tains of North Carolina where those four MATERIALS AND METHODS forms occur sympatrically. Both authors This study is based mainly on Organ's found that, in the order given above, these series of Desmognathus from the Balsam species form a series in which decreasing Mountains. With regard to the species size is paralleled by an increasing tendency wrighti and quadramaculatus, I restricted toward terrestrial habits. Organ further this study to these series. I have included found that the trend is also paralleled by specimens of D. monticola from western increasing juvenile survivorship. He con­ North Carolina in addition to specimens cluded that heavier juvenile mortality is from the Balsam Mountains in an attempt to associated with aquatic sites, and that D. include more of the total snout-vent length quadramaculatus, D. monticola, D. fuscus, range for that species. Data on series of D. ochrophaeus, and D. wrighti represent D. ochrophaeus from the vicinity of High­ an evolutionary trend in which selection lands, North Carolina and D. fuscus from has favored progressively more terrestrial Licking County, Ohio are included where habits. comparisons with Balsam Mountain ma­ Size and egg production are positively terial of those two species are appropriate. correlated in the genus Desmognathus, as Whenever possible, only females with they are in many animals. Organ (1961) eggs greater than 1 mm in diameter were also emphasized that the larger species lay examined. Otherwise it was difficult to larger clutches than the smaller ones, and distinguish smaller eggs from those to be that the evolutionary trend within the deposited the following year, since in the EVOLUTION 22:806-816. December, 1968 806 SIZE-FECUNDITY RELATIONSHIPS IN FIVE SALAMANDERS 807 early stages of yolk deposition egg sizes Harrison's work indicates that annual egg are so variable as to obscure the differences laying may occur in D. aeneus. The evi­ between the clutches of successive years. dence for bienniality in Leurognatkus is Snout-vent length measures the distance not, in my opinion, compelling. In view of from the tip of the snout to the posterior these arguments it would seem dangerous angle of the vent. The method of covari­ to assume bienniality in D. wrigkti, D. ance analysis was utilized to compare the monticola, and D. quadramaculatus. While slopes and elevations of the regression lines more data on this point are sorely needed, for the five species, using the methods and I shall assume all five species dealt with forms of calculations given in Snedecor here to be annual reproducers. (1956). The squared deviations and cross products of deviations were calculated from Nesting Habits computer calculated raw sums, sums of All five species exhibit parental care, in squares, and sums of cross products. In which the females remain with the eggs the case of D. quadramaculatus rounding until hatching. Pope (1924) found that error prevented the use of computer calcu­ females of D. monticola and D. quadra­ lated raw sums, and hand-calculated sums maculatus attach each egg individually to were used instead. the roof of the nesting cavity so that the eggs form a flat mass one or two eggs thick, SUMMARY OF HABITS AND whereas D. fuscus, D. ochrophaeus, and D. LIFE HISTORIES wrigkti (information on the latter species The following accounts are based pri­ from Organ, 1961) generally deposit their marily on the studies of Hairston and eggs in spherical clusters with only a few Organ, supplemented in certain cases by actually attached to the roof of the nesting my own observations. cavity. Females of the five species utilize some­ Female Reproductive Cycles what different sites for egg deposition. D. Organ concluded that all five of the spe­ quadramaculatus utilizes the most aquatic cies deposit eggs biennially, but Martof sites, depositing eggs on the undersides of and Rose (1963) found evidence for an­ rocks in the beds of streams and beneath nual egg laying in D. ochrophaeus in the small waterfalls. D. monticola, D. ochro­ southern Appalachians. Tilley and Tinkle pkaeus, and D. wrigkti deposit eggs in less (1968) have presented evidence for an an­ aquatic sites than D. quadramaculatus, be­ neath stream banks and, in the case of D. nual or possibly even biannual cycle in D. ochrophaeus in the vicinity of Mt. Mitchell ochrophaeus, beneath moss on rocks and and in the Balsam Mountains. Spight logs in seepage areas. D. fuscus appears to (1967) concluded that D. fuscus deposits lay eggs in situations intermediate between eggs annually in eastern North Carolina those utilized by D. quadramaculatus and and Harrison (1967) found that a sixth those used by the other species. species, D. aeneus, also lays annually. Martof (1962) found evidence for biennial Lengtk of tke Larval Period reproduction in another desmognathine, The length of the larval period varies Leurognathus marmoratus. greatly among the five species, and reflects The same weaknesses which Tilley and the aquatic to terrestrial trend discussed Tinkle found in the arguments for biennial above. In the terrestrial D. wrigkti meta­ egg laying in D. ochrophaeus probably morphosis occurs prior to hatching (one apply as well to D. wrigkti, D. fuscus, wonders, therefore, why it deposits its eggs D. monticola, and D. quadramaculatus. in aquatic sites). Organ gave estimates of Spight's study bears this out for D. fuscus. 26-28 months for D. quadramaculatus, 12- 808 STEPHEN G. TILLEY 4.0 3.5 0 Z ...w U ... 3.0 0 u. o· 0... 2.5 2.0 3.0 3.5 4.0 4.5 LOGe SNOUT -v ENT LENGTH FIG. 1. Relationships between size and fecundity in five species of Desmognathus. Lines represent least squares regression lines of log. follicle number on log. snout-vent length. 13 months for D. monticola, 13-16 months cola prefers the banks of streams, as does for D. fuscus, and 10-11 months for D. D. fuscus. Organ found that both D. ochrophaeus. The estimate for D. ochre­ ochrophaeus and D. wrighti occur in ter­ phaeus is in error (Tilley and Tinkle, 1968); restrial situations. Males of both species the larval period of that species is from 4 are largely terrestrial during the summer to 6 months at Mt. Mitchell, North Caro­ months, moving to aquatic sites such as lina. seepage areas and spring heads during the Age at Maturity winter. His data, as well as Hairston's and Organ estimated that males of all five my own observations, indicate that of the species matured at 3.5 years of age, while two, D. wrighti is the more terrestrial. The Spight (1967) estimated 3 years for males aquatic sites preferred by D. ochrophaeus of D. fuscus. Both authors concluded that are of the seepage area-spring head variety, females require an additional year to pro­ rather than the stream or stream side habi­ duce their first clutch of eggs. tats occupied by D. quadramaculatus and D. monticola. Habitats The species are also segregated altitudi­ D. quadramaculatus occurs chiefly in nally to a certain degree. D. ochrophaeus larger and faster streams, while D. monti- occurs from the lowest to the highest avail- SIZE-FECUNDITY RELATIONSHIPS IN FIVE SALAMANDERS 809 TABLE 1. Summary of regression data. n =sample size, r =correlation coefficient. Equations and correlation coefficients are for regressions of log. foUicle number on log. snout-vent length. v = Balsam Mountains (Virginia), 0 =Ohio. Significance Regression Species " level equation D. wrighti 23 0.458 0.050 Y = 2.4130X - 5.7235 D.ochrophaeus 25 0.598 0.010 Y = 2.1773X - 5.1407 D.fuscus (v) 26 0.837 0.001 Y = 2.2845X - 5.2727 D. [uscus (0) 18 0.687 0.010 Y = 1.7484X - 3.3944 D. monticola 35 -0.163 < 0.100 D. quadramac. 26 0.390 0.050 Y = 1.0700X - 0.8825 able habitats in the Appalachians. In the sion lines relatively homogeneous, but not Balsam Mountains D. fuscus has a similar in removing all of the curvilinearity. D. distribution, but does not extend as high wrighti appears to have somewhat higher as does D.