In the wood frog (Rana sylvatica), the interior of the globular egg cluster has been found to be up to  warmer than its surroundings, which is an advantage in its cool northern habitat.
ɪnðə wˈʊd fɹˈɑːɡ ɹˈɑːnə sɪlvˈæɾɪkə, ðɪ ɪntˈɪɹiɚɹ ʌvðə ɡlˈɑːbjʊlɚɹ ˈɛɡ klˈʌstɚ hˈæzbiːn fˈaʊnd təbi ˌʌp tə wˈɔːɹmɚ ðɐn ɪts sɚɹˈaʊndɪŋz, wˌɪtʃ ɪz ɐn ɐdvˈæntɪdʒ ɪn ɪts kˈuːl nˈɔːɹðɚn hˈæbɪtˌæt.