Primary and secondary phenology. Does it pay a frog to breed early?

Jon Loman

Research output: Contribution to journalArticlepeer-review

16 Citations (SciVal)


This study examines the consequences of variation in the laying and hatching date for
the time of metamorphosis in the common frog Rana temporaria. Field data are
presented showing that eggs laid early tend to take longer to develop. Thus, the time
advantage for early eggs is reduced at the time of hatching. There was an among-year
variation in this phenomenon; it was not manifest in a phenologically late year. Also,
field data revealed that mortality due to pond freezing is a real risk for early laid eggs.
Finally, two experiments in tanks analyse the effects of hatching date variation for
the time of metamorphosis. (1) When hatching was experimentally delayed by 7 or
11 days, this resulted in later metamorphosis, however, by only 2 and 5 days,
respectively. (2a) When tadpoles from the same pond that naturally hatched at
different times were compared, it was found that a hatching time difference of 6 days
resulted in later metamorphosis by 2 days only. (2b) A comparison of tadpoles from
two different ponds that hatched 11 days apart also resulted in only 2 days’ difference
in metamorphosis. In this case, the later but faster developing tadpoles metamorphosed
at a smaller size. I suggest that eggs from these two ponds differed genetically
in the growth and development strategy. Despite the obvious risks, and the moderate
gain in terms of early metamorphosis, frogs breed dangerously early in spring.
Possible reasons for this are discussed. These include external selective forces that
promote early metamorphosis (also at a high cost), within-pond competition among
tadpoles with an advantage for early and large tadpoles and finally factors relating to
mate choice at the breeding site.
Original languageEnglish
Pages (from-to)64-70
JournalJournal of Zoology
Issue number1
Publication statusPublished - 2009

Subject classification (UKÄ)

  • Biological Sciences


  • metamorphosis
  • hatching
  • freezing
  • breeding time
  • egg
  • R. temporaria.


Dive into the research topics of 'Primary and secondary phenology. Does it pay a frog to breed early?'. Together they form a unique fingerprint.

Cite this